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DECEMBER 1981 







• 



Vol.1 No.5 



Video games 
for Christmas 

Review: 
ZX printer 

Chess end-game 

ZX-81 strings 



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Computers in schools 
More micro music 
ViC-20 cassettes 





£?__Aj1 




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Ki .^kS^S 



Make the most of your 
Sinclair ZX Computer... 

Sinclair ZX 

software 
on cassette. 

£3 H — per cassette. 



The unprecedented popularity of 
the ZX Scries of Sinclair Personal 
Computers has generated a large 
vi i lume i if progra ms %vrincn by users. 

Sinclair has undertaken to 
publish the moM elegant of these 
on pre-recorded cassette*. Hach 
program is carefully vetted for 
in [ere st and quality, and then 
grouped with other programs to 
form a single-subject cassette. 

Each cassette costs £3-95 
including VAT and p&cp) and comes 
complete with full instructions. 

Although primarily designed 
for the Sinclair ZX8U many of ihe 
cassettes are suitable for running 
on a Sinclair Z2E80 - if fitted with a 
replacement 8K BASIC ROM 

Some of the more elaborate 
programs can be run only on a 
Sinclair ZX Personal Computer 
L m Lamented by a loK-bvtc add-on 
RAM pack. 

This RAM pack and ihe 
replacement ROM arc described 
below. And the description of each 
cassette makes it clear what 
hardware h required, 

8K BASIC ROM 

The 8K BASIC ROM used in the 
ZX81 is available to ZX80 owners 
as a drop-in replacement chip. 
With the exception of animated 
graphics, all the advanced features 
of Lhc ZXfil are now available on a 
ZX80- including the ability to am 
much of the Sinclair ZX Sufi ware. 

The ROA1 chip comes with a 
new keyboard template which can 
be overlaid on the existing 
keyboard in minutes, and a new 
operating manual, 

16K-BYTE RAM pack 

The IGK-byte RAM pack provided 
l6-tiwie$ more memory in one 
complete module. Compatible with 
the ZX81 and the ZX80, it can be used 
for program stoiage or as a database . 

The RAM pack simply plugs 
into the existing expansion pon on 
the rear of a Sinclair ZX Personal 
Computer, 




Cassette 1 -Games 

Pbf ZX8I fmdZXSO with 8K 
BASIC ROM) 

O REIT - your space craft's 
mission is to pick up a very valuable 
cargo that's in orbit around a star, 

SNIPER- you're surrounded 
by 40 of the enemy. How quickly 
can you spot and shoot them when 
they appear? 

METEORS - your starship is 
cruising through space when you 
meet a meteor storm. How long can 
you dodge the deadly danger? 

LIFE -J. I I.Conways 'Ciame of 
Life' has achieved tremendous 
popularity in the computing world. 
Study the life* death and evolution 
patterns of cells. 

WOLFPACK -your naval 
d est rove r is on a sub ma rmc hum. 
The depth charges are amied ? but 
must be fired with precision, 

GOLF - what's your handicap? 
It's a tricky course but you control 
the strength of your shots. 

Cassette 2 -junior 
Education: 7-11-year-olds 
«r ZX8t mthteK RAM pack 

CRASH - simple addition -with 
the added auction of a car crash 
ifvouget it wrong. 

^MULTIPLY- long multi- 
plication with five levels of 
difficulty. If the answer's wrong* 
the solution b explained, 

TRAIN - multiplication tests 
against the computer. The winner's 
train reaches the station first, 

FRACTIONS - fractions 
explained at three levels of 
difficulty. A ten^question test 
completes the program. 

ADDSUB- addition and 
subtraction with three levels of 
difficulty. Again, wrong answers 
arc followed by an explanation. 

DIVISION - with five levels of 
difficulty. Mistakes are explained 
graphically, and a running &corc is 
displayed. 

SPELLLNG-up to 500 words 
over five levels of difficulty. You 
can even change the words yourself, 

Cassette 3 - Business and 
Household 

Par ZXSt |W ZX80 zriiti SK 
BASIC ROM) iriib 16K RAM pack 

TELEPHONE- set up your own 
computerised telephone directory 
and address book. Changes. 
additions and deletions of up to 
50 entries are easv. 

NOTE PAD- a powerAiL casy- 
to-run system for storing and 




retrieving everyday information. 
Use it as a diary t a catalogue, a 
reminder svstem n or a directory. 

BANK ACCOUNT- a 
sophisticated financial recording 
system with comprehensive 
documentation. Use it at home to 
keep track of *where the money 
goes/ and at work for expenses, 
departmental budgets, etc. 

Cassette 4 - G antes 

For ZXS1 (and ZXSO &uh SK 
BASIC ROM) and 16K RAM pack 

LUNAR LANDIN r G-bring the 
lunar module down from orbit to a 
soft landing. You control attitude 
and orbital direction - but watch the 
fiiel gauge! The sc re en displays your 
High t $taru*-di0 ia| |y and £FiphicaJly. 

!TO=\TYO\T- -a dice version 
of Blackjack, 

COMBAT- you're on a suicide 
space mission. You have only 12 
missiles but the aliens have 
unlimited strength. Can you take 
12 of them with vou? 

SUBSTRIKE-on patrol, your 
frigate detects a pack of ID enemy 
subs. Can you depth -charge them 
before thev torpedo you? 

CODEBREAKER-ihe 
computer thinks of a 4-digit number 
which you have to guess in up to 10 
tries. The logical approach is best! 

MAYD AY - in answer to a distress 
call, you've narrowed down the 
search area to 343 cubic kilometers 
of deep space. Can you find the 
astronaut before his life*support 
system fails in 10 hours timer 



tscttc 5 -Junior 

Education: 9-11 -Ids 

ForkXSl andZXi 
BASIC ROM 

M. VI "HS- test si- 
three level i of difl nd §i ve* 
your score out of 10. 

BALAXC E - tests ur; z r> ur.d ing 
oMcvers fi^crumthe* t - 

series of grar"-- ~ * ■ ' 

VOLUMJ - 

answers from thl 'tr to a 

serie * of cuoe vo i _ . \ onSv 

AVERAGES ■ rage 

h ei g ht of y our dm \ ■ : rage 

shoe SKe of your sarrj^ 31ge 

pocket mune> : . The 
:omputerplf»> ahaf ehatt wd 

disring^hesMkAN :- [AN. 

BASES -convexl it ~ :r.::ral 

(base 10 tOodi our 
choice in the ft rig 

TEA! P - Vol urr t - res 
-and their comtnnat] 

How to order 

Simply use the uT-lt: I ra 

and either enclose j ch?^ : eive 

us the rmrnhc* ! 

Ba relay ci rd or Truit , - ant 

Please allow 26 di*i fry 

1 4-day money -h,;,* 

Sinclair - 

ZX SOFTWARE 

Sinclair Research Ltd, 

6 Kings Parade. Cambridge. 

Cambsi., CB2 ISN, Tel: KT7S «61frL 



I To=Sitwlj^R*r%r»rch.FKF_l-.PoSrr7,CjfflbfLJ t ^ I R2 m 
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*Z& BASIC ROM rr. i ZXSO £ \ B.lti 








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*:' ^.in.i; >.-.: ■.: :::... j- ■: £lSi 



Toid£ 

" Pkw idd (2.HS id total oid t: Hi uc Only ilonJennit ROM indoor RAM 

I cnrltHC 4 cheque /J*tl tuSinti jir H-nejivh Lid iat& ^^^ 

PIcjk chir^c my Accctt" fUrdajcurd "TnitlcarJ no. 

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YOUR LETTERS: 

ZX cassettes, Sinclair machine code. 




12 



NEWS: 

Japanese deal for Sinclair, Vic-20 peripheral?. 

COMPUTER CLUB: I / 

David Pollard visits The Nouing Dak 
Technology Centre and discovers Us origins. 

VIDEOGAMES: "J 

A review of rhe main video games on sale for 
;;Christmas, by Selwyn Ward. 

ZX PRINTER: ^TT 

Brie Dees on and Stephen Adams test th£ new 
ZX primer and ask if ii really is worth £50, 

ITERVIEW: ^O 

Sill Bennett talks to Richard Fothergill who 
ins the Government's micro project. 

CHESS: %J\) 

John White presents a program for working 
trough the end-game, and Phillip joy relates 
low he wrote his program for the ZX-80/8 1 . 



MICRO MUSIC; OD 

In two articles we present a range of idea* and 
programs for generating live music on the 
Tandy TRS-80 and the Sharp MZ-80K. 

ZX STRINGS: T 1 I 

Graham Thomson explains how to make full 
use of those space-saving string functions. 

EDUCATION: T"Q 

The Government plans to have a micro- 
computer in every school by the end of next 

year, Eric Deeson presents some of his own 
ideas on how these machines should be used, 

VI02tt PROGRAMMING: Q O 

Nick Hampshire explains the use of the 
cassette recorder on the Vic 2 ft. 



56 



ATOM DISASSEMBLER: 

Roy Burgin presents a disassembler program 
for the Acorn Atom. f*f\ 

COMPUTER CONTROL; OU 

This month j John Dawson describes how he 
set about wriiing an interpreter for his 

machine. 



RESPONSE FRAME: WW 

More answers to your technical queries. 

FINGERTIPS: OD 

David Pringle presents some more thoughts 
on programming calculators, discusses last 
month's program and introduces some new 
games, 

BOOK REVIEWS: D W 

ZX-81 machine-code, video computers, Atomj 

theory. 

SOFTWARE FILE: / 

Seven page* of programs. 

COMPETITION CORNER: O I 

A £1 5 book token is the prize in our Christmas j 
quiz, and we reveal the solution to ZX-81 
crossword competition. The ZX printer 
cross wotd falls between pages 14 and 15. 



Cover photograph by Stephen Oliver. Oor thanks 
to the Siticp Shop [offending us the video games ; 

for the photograph &nd the review. 



: 



Editor 
DUNCAN SCOT 

Staff Writer 
BILL BENNETT 

Production Editor 
TOBY WOLPE 

Production Assistant 
JOHN LIEBMANN 

Editorial Secretary 
LYNN COWLING 

Editorial: 01-661 3500 

Advertisement Manager 
DAVID LAKE 01-661 3021 

Assistant Advertisement Manager 
PHILIP KIFBY01 661 3127 

Advertisement Executives 
KEN WALFORD 01 -661 3139 
BfLL ARDLEY 01-661 3127 

Midlands Office 

DAVID HARVETT 021-356 4833 

Northern Office 

RON SOUTHALL 061 -872 8861 

Advertisement Secretary 
MANDY MORLEY 

Publishing Director 
CHRIS HIPWELL 

Your Computer, Quadrant House, The 
Quadrant, Sutton, Surrey SM2 SAS. 
Typesetting by in-Step Ltd, London EC1. 
Printed by Riverside Press Ltd, 
Whitstebie, Kent. 

Subscriptions: U.K. £6 for 12 issues. 
©IPC Business Press Ltd 1981 



Pubfihed by IPC Etactrlcal Electronic Prtsa Ltd, Quadfani 
Hautt r The Qudcrrj.nl, Sulion, Surrey SM2 5A5 Teh 01 Efil 
3600 Tfllipi-grirrtt; S&20&I BlPRHG 



EDITORIAL 



THERE IS A PL AM to impose an extra charge on the cost of blank cassette tapes — the 

medium most of use to save out lovingly-created programs. One might argue that cassettes 
are expensive enough already, especially if one always plays ii sale and keeps a back-up 
copy of every program. 

The proposal originates from the British Phonographic Institute (BPI) T ihq industry 
association of record manufacturers The industry has been in a steady decline sinc£ its 
days of heady success in the sixties. Sales of records, LPs and singles, have fallen and a 
number of record-producing companies have gone to the wall. The reason, so the BPI 
argues 3 is thai too many potential record buyers have chosen to break the law of copyright 
and tape their favourite records. 'Phis* the BPI says, robs the industry of its just rewards., 
and deprives the original recording artists of royalties. 

The BPI believes it is powerful and influential enough co persuade the Government io 
include the levy proposal in the forthcoming revision of the taw of copyright. 

There are • number of objections to this proposal. The first is that ii will cost money to 
implement and supervise the levy — money which is effectively wasted. Secondly, it will 
be left entirely to the discretion of the record producers how to distribute the proceeds — 
there is no guarantee that it will be fair and equitable, Thirdly, some tape manufacturers 
may try to avoid paying the levy by selling tapes of Argentinian dance music on w r hich 
there is no copyright — the user could easily record over these. 

There are other reasons why the proposal is bad. For the last ID years^ perhaps longer* 
the record industry has been producing consistently bad-quality pressings, distorted 
records, records with scratches and bumps on them from the moment they were pressed in 
low-quality vinyl. The quality of the products has been so poor that it has often seemed 
hardly worth the bother of buying a record, knowing (hat it would have w he relumed. 
Because of the failing sales, the prices have been pushed up in an attempt to slay 
profitable, thereby trapping the industry into a circle of decline. 

Now, rather than improve their own quality control, the companies look to a levy, 
raising extra cash from the wide section of the population who use blank tapes quite 
legally. We think this is wrong and would like your help io campaign dgainsi i[, Please 
either write to your MP, or your locai or national newspaper* Or else write to Your 
Computer and we will forward copies of your letters on to a number of MP* who will be 
taking an interest in opposing this proposal. If your response is large enough we might be 
able to stop the proposal getting off the ground. 

The NEXT ISSUE of Your Computer witt cost 60p and the price of a subscription mil rise from 
£S to £8, Ifyott uwnt io subscribe f<? Your Computers do it before tft<? end of tti£\*ar and you 
save £2, 1'ftcre is a subscription card between pages 8§ and 87 of this tnogttine* 9 



VOUR COMPUTE DECEMBER 196 1 3 




MV1 - a 200 computer for £105 



VAT 



TheMVl computer kit uses She ybiqurlousNOscom 1 PcPandFhe 
Z80 C^U Interfaces are included for television, printer and cassette 
2K memory, Gemini power supply (anves up to 3 extra boa Eds). 
ChwiyfuH ASCII keyboard and Quantum Graphics are olso 

included. Available with etth^r on ASClF version ol the 
NOs-Sys 3 monitor. Of a Tiny BASFC, 
MV1 is expandable Gemini 
80-eUSspecrfcaTicn 



MieroVal ue's 
'Nascom Special' 



WE £10750 



SAVE «,, . 
OVER £65 

We ' ve put i ogeth er a micro* ; ompu I er kri co nf o hmg Th e No scorn 2 , 
U a &-Sy s 3 , Gra p h ics ROM , Bits 4PC"j progro rn me rs a id , Gem in j 3 
APSU 16K GAM Board and rrilrilmorhar&oord Theresulfiso 
powerful micro using marker proven boards and components. 

RRP OVER £405+ VAT 
MicroValue price 

£340 




VAT 



SHARP MZ80K with 
Super Graphics 



SAVE 
£200! 



The 4a K R AM System i s ofte? * a at a rock bo Wo m pnc e wit h the 
Quantum Mpcros Hi Be&Graphcswtnch gives resolution downioo 
single dot and high res. plotting Characters a re user definable and 
the Oi*el characters actually jom live tt ee games packages are 
included tool 

*Rf» t*45 -VAT 
MIcftAMufr price 



£445 



VAT 




f QA wortti of accessories 
2**311 FREE wfth every 

Epson Printer 

Epson MX80T.„. „..„ ,„....„„. £359 - vat 

Epson MX80FT1 ., £399 - vat 

Epson MXS0FT2 .„..„.„ ^, £465 - vat 

Epson MX i 00 _.*>>+***** — £575 va* 

Buy one of the above Epson s from MicroVolge ond weH 
glveyoua Pack otFanfo»d pa oer. Spore Ribbon Cartridge 
Interfacing Document and Connecting Cord for Murtiboarc 
Of N.o$com The occessones 
are worth S30 out you 
con hove them 



PPSkofc'. 



CWSK«* 



SAVE 

£156 



Nascom IMP + Graphics 
Only £199. vat 

Min'ovotjehos siasheo the price of the eOcps 31 _ i IMP dot 

motnx printer And odded imprint's high res graph ■ c u p 3 double 
width c ha rocte? option fMPhas dc*ci« vat 

SKff flnfl S^XS:* 5 

£199 VAT 



NASBUS Compatible DOUBLE 
DENSITY Disk System- 
Available Ex Stock 

With hundreds in dairy u$ethe Gsmim Disk system is now 
rhe sianaa rd tor Nose om o n d Gem i n. M u ttipoa ■ d sy ste m s 
Single or twin drive configurations ore available, grving 
350*< storage per dfrvs.Tne CP/M 2.3 package sup pi iea 
sjpoorH onscreen editing with either the normal Noscom 
Or Gem in : ivc screens, poroHel or serial pnnlers. and aula 
stngle-douDte density selection. An optional alternative I o 
C p7m is a va i I a bte f or N ascom owners wishm g lo supp o n 
existing software Copied POLYDOS 2 h includes an editor 
ond assembler ond extends the Nascom BASIC to indude 
OhSkGommand*. 



Single driv* mfem 



£465 



VAT 






Double drlvfl system 
(GIO^ ©615/3) 

£690 vat 

CP/M 2.2 packoge 
(G513) 

£100- VAT 

Potydo* 2 
£90 - VAT 




4 YOUR COMPUTER, DECEMBER 1381 




MV2-TWIn 



&&* 



Controlled Development Computer 

The fy fly buiW and tested MV2 microcomputer is controlled by two 
ZflOA rn ic ro p roc eisors J ntortacos include HS2 32, cassette. 2 h flbit 
pa mJiei ports, and graphics including programmable graphics. 11 
provides 80 - 25 screen formal and include 64K RAM, Int&grol PSU 
and Ml ASCII keyboard 

Software written to run under the RP/M ROM po&ed monitor can 
&e transferred lo disk to run under CP/M a! g later date. This rugged 

CQtnpute" 3S ideal tor 
educational and *ndu s? nal 
environments and Js 
supplied with the 
a vanc^d CO M AL 
structured BASIC. 

SAVE 
£76.50 




Mte ro Value price 

£595 



VAT 



MV3-Low Cost 
Business System 



SAVE 
£91.50 



A complete, fully Duiit do u bie dis k bo sed CP/M vers ion of MV2 

system Supplied wrth VDU and keyboard. Full CP/M software library 
available. __ . ■ 

The MV3 is a highly reliable system of MicroValu* price onry 

moduio tor internal construction backed by j&A C E ^% 

th e f u 1 1 Mic ro Vo I ue wo rra nty X# 1 W w W - VAT 





MV3WP System 
Word Processing 
System for only ' 

£2550 vat 

By combining the power o* the 
MV3 and Itie pop jfar C P- M word 
processing package word star, and 
then adding tne Oiympio daisy 1 
wheel printer, we con now offer 
a system for computerised 
letter and *epGfl writing, 
catalogue and price list 
compilation, elc etc. as well 
os handing all the data 
processing tuncf iom 
crftheMV3 



MicrcVaiue 

Business Software Package 

A fTjUy integrated business package is ura Noble toi the MV3 
and MV3WP systems and includes Sales, Purchase, and 
Mommal ledgers and Slock ControJ. plus all &Af\f\ \ 
documentation MhCroValue price X#4UU I 

• vAtJ/ 



New Software for Nascom Systems 

PQLTOO& * A dnh owoNng syUCKn Kn JIG wfltn N«eom 1- 0* 2anfl G*m*m GftOi 0** 

Syilern * An hnccTipg 'op** a p-d * rtrprapty ¥r#4l p^ign 1 "**? C^OS lt>ol i^ i^oV* gn frdifl* or*G 
Oit#^b^ □ no 3O0* ditt cc^YMMindi to t^# Nqko^ B*£*C *Vttt«**oJufl p*ce t*0 - VAT 
MATHS PAK OfluC^e pr« isi^r. mo'hj poc fcgy* or. low MncroVoi je pn^* fcl £ - VAT 

MATHS PAX Hand!** UlGd in-conpunebon wi-h y.ATH5.P4«t Mlc>d*Hu*pne# tv 9S p VAT 
Cejftrt^nor.d fc*t»ntf»r r-pj yn* ■uirn MATH5PAK h Qrt$nd£ &A$IC f tttwvQ wortf*! 1 

MfcrdVaiu* ^ict E*.^S - VAT 
l£gk Ml B*Ujerf»f aj^ «nrfrjigrtPd owpmo* a^o auoum biff pa ttog>§ whists allow* 
Oitcise-r S' T 3nrJ r*Ds*ernQ.y ffc^qpiywrttfi^o-n rrtfl m^ncfyrriop 

MicioUolutpflc* Ktf-UU 

Standard Firmware for Nascom of Reduced prices 

N45FEN tTOPSH-VAT Mk rtAfaSu* pn* * £30 - VAT 

NQ4^*3 « RftPUS-VAT Mh^WiSu* e*^t «0 -VAT 

fcQiDi* - B JO £t PGOMJ HfiPt§0 - VAT Micnttat u+£MK* £50 - VAT 

Hoi&i r>Byg{TAPE) . . M»ii3 ■ VAT MkrtpVo^* Oftt* tSO - VAT 

impnnl fi&Pt J3 - VA1 M^raVolL* price tSO - VAT 

ftisiPCB^gg AiO t3* - VAl UpCOVoI l* price t20 - VAl 

80 x 25 Video for Nascom 

Nascc-m o^^C^^O*^^ a ptMcinonoi BQjt 2&VidftC aftOkSv b^ 1 ui*rvg pn*G^n»ni 
&fi^ ? Inlukige-^ V-dftQ C ? <h v^^ Q*-\&QQ T a I &&a Tni> to "" f>QQ$ nal QCC yPv lyile-r- 
m*FT>Qi> ipoc^Q -1 ^ prdwidcjoviar&C uier^o ri! TPllot3 B e bncilDnsiriciii^Sing piog 
cha'acle^ ie" Hjsv cofnDant>te w^r, G-er-un-SMS an-a SB^£ 'B W t>W. lyllftmt 8u*0.ne 

bits* PC'S target electronics 

4 Westgate.Wethefby.W.Vortcs. 16C*>erTytarw, W^olBSt 3NG. 

lel:(0937}«7M. T»l:{0a72)421fH. 

INTf RFACE COMPONE WTS lTt>. 

BfCTBOVAUIE LTD. Oa Weld Corrw^Syco more toad r 

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Manchester M19 1NA. To k (0240 3) 22307TU:ft377»», 

T#(;(0M)«1 4*6* HENCY'S RADIO 

2 8 St J udes , Engleti eld Gnten , 404 Edgwo re Roa d H London W2 . 

EgrTQm.SurTey TW300HB. T#k:fOl) 402 6B22. 

TeF;(07ft4) 33603. Tlx;264475. Tl«i622&4 (quote r«f:«00). 



^MicroValue 
Warranty 

All products GkCGpikits.soJdby 
M^c revalue deoiers are supplied with 
1 2 months" worraniy and will &e 
replaced or repaired 5y ony deoier 
(ev^n if you didn't &uy it horn hr.nn) ir> me 
group m the event o* IouItV rnanyfackjfe 



YOUR LOCAL 

MICROVALUE 

DEALER 

All Ihe pr»^c»i on tr*« Jtoo poflti 
0^ ■MJi-flC'^ w^ilt AM -it* ^*ff ^pn< 
1h« MifPWIuf *0frTi UStM Ph.ngftf 
(M*i^» flflQyi 1 ^* liXXJi-3 

o « ciacfc^ My*^. ,i Acflws ana 

Borrloy«fl?^wcon# 



V0UR COMPUTER, DECEMBER 1»J 5 



jgJjjEl^^ 11 * THE NEW Et 




H.£XC/77/VG| 
TRS80 
MODEL 
III 




48K 
p£619 *i 



Thi ftaita Shack T p$ SCi™ ModH m * a ROW based 

Ctfmpulif VAlcm CQm4ting nl 

• A 1? ir*c«h sown to drieliv f«u-lii ind ejr*t ipftyinif-iati 

• A 65 iw tamo* keyboard for in pu I ting projramund data 
10 Ihi Compulttr • A Z S3 Micro&rrxesSDr. !hfl beams." of 
it* &v*it*» #A Hfcd> lirrtb- Clock * ftead Only Mefnety 
<RQM^ containing lhe M^drl II' 9 ASIC L^nijjaoa Mully 
CCWIKMIiBlfr *>rh fnoil ModtH ! B-ASlC SWOflfiM"Ii •Bj«dom 
Accwwl M«*m^rv" ''RAMI' 1in iLi^Jyh* n1 nrnur.im* nnil clnl;t 
wH-tt line C<>m[>yi*f h nn ^amount tf **pand»W» 1>fl*n " W 
to "-titti", cn>[it>iwil r^trji * ACawttff kilwftotlorto^n ic*m 
\i&r*q* of programs and data i''equpf« a wcarata ca«*1ti? 

itCQfAi, Opwml.'aXH-tr • A Prjn.fflr ln«jtf#C4? 'iX Kairf C-OOY 
CHJTDutd CrOurini* -nd ddld Iiimjuiibi j m^ihV ■ hl- p- ul<=- 
OfJl"Onal, , «*l'*l aiEhpani-on area for upflrjdirig tfJ a d'St 

tnund lytiom I rjfHiontW oxira I • E* pa 11 * 'o* - . rjrgj Fqt an R 5 

232- C i*riai EEwnmun#tatlo*w m1#rface ■lonliorLai *Mra! 

All Ihw tompOnantf if* «*Wn*d ^ i lil^it mOukJ#d U«, 

and «h iru power ad wa on* pnvtr cord . 

Dm Dfiv« Kn *i;n 2*4ti Track D 1 ^** - CM +VAT 
Di« Drives Kif ^ii[n 2i.EE Track Drives • £72i a vAT 
Add CHj ro' In^tiiNt'On 




£369 ,.;, 

including c«b4*t 

Siandaf d F«*lurai 
* hk 1 CFS F^GHrbanal 

Spacfed M*>d* *W CPS — 
Monmaand Mode aPiwerWmal SpKaji Pm* 10 CPI 
jrxJ 16 T CPI Ihi^ StV*pn r »-0"JU Of 7 Jl B iMoooapKldl 

Dor MAi'i- • ? * S Dor. M#id,b * 3 itVjy PauM HamttMu 
£y*I*™ *4S tiuracwi ASC 1 1 pfeis 6 European ctiarat Icr 
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Mar^n JiiSJUfiCa&on • Pf -rtf Undqriinmg #3 Wtf€ Fh» f "%*! 

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Sn»r!P[3 • Pjp^' Tfeaa Qar * tr*»ir*P»H: CoKHiri and L QQO 




MICROLINE 80 



£299 



• eCLfi*Ufn dt^cciufjnji * Small n/e 3^2 iW> ■ ?M iQI ■ 
lfJQ I Hi mm * TrjTJ C-Ti*ric(pr>. 4$ ft &C I and 64 graphic* * % 

Ouracra-r ma^ 40, SO or 132 elwi.-'hrH • r-ncrion 
and f»n frtPtJ • LaVv [*ii.i>»*; SS <!B • LOW ^«i0^! fi 5 kg 

MICROLINE 82 £449 *v*r 

IKICpl a.-H-rtilEtfinai 4jc^c s«k,n y * Sm^ll n«i 3W lW' 
- 32fliDi h ISOLHUnm. ailUciwacwi, 9eA$CEFaAdfi4 
giaohciL w|h 10 Mationo* ctiaraclrr-i«l Vanar>Ei ** 
CtuvacTn tifi^ <0, W. » e* 1H frh#Pihnt^ *6yi^'ift 
Hnifi anfl aatial ^-irrlit« « Frtfion «nd Pm Facd 

• Low noiM' 66cia * Lcnar tfr&ghi. fty 

MICROLINE 83 £773 vat 

• l£Q tpa. O d*«iBOnaf logic ««k>ng • 136 Lulumr', [ir^Eing 
OAypId Itnlfrrm* # SftvilF *u* St?ltVl * SSlQl * 1 3tl 
III) mm »1fjCchii«Hf*v , »ASCiijrid64^apn B Gi wth r0 
Hal«nol ?h4^aci«r tei var^ma *1 ClvrjKhv ip»ci"g* i. 10 
and 16 5 CMirt m O-ftj-ii m QmMM and uiuf Inlerfatra 

• Fncfeon and Pjrt F44d * Lo** nont ft&dB * Low 
13 kg 



si° 



c^^* 



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to»^ 



r-l EUROPE S FASTEST SELLING ONE BOARD COMPUTEP 

rOMPUKIT UK1Q1 



v*- &1 



* Wff? iwi^d 1 4*»iKm ten -vofciE lor 
fflOMy on ihe Turh*i « PoA**tw> BK 
&»■<: - Fittrcj afownd a Ful Gw*4Tv 
Ke^toi-d * IK RAM EEpaAdao% io l* 
■on IXHI" i a Power «uoptY «f«J Nl 1 
Moduiji0f on boapd • *io E«lr» 
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Tdp>e in-eriace oii board * Fit* 
Samp «f Tap* including oo^ftiul 
Chiw^wmnif * and Won*fjcj* »m aath 
K>T * If ynu wa^: to >*arn about 
M-c^o». bwf OJn't tn&w y*h<is wucftint 
"o- ouv [hn n [h4 4 [h# jnacJw for vou 



1 r<iiSK*S? ! "' sl 




-"^s T »" 



JA FREt NEW 

M?*rTo n i-ISLm,,, 



- Sc#e„ n fdl(lkii 



kit only £9fl,95 



Fully AsftombMd - flff * VAT 




NEW MONITOR IN ROM - *>+i*lto Mparai*^ at fT.10 - VAT 

Im^iu^eo B*i-e luneii^ - ^a«a«d GARBAGE poulm* AUowt co/r*cr u« s» STRING .A HP '. ^ S C*» 

Th.ii crip can o* *o4d woaiata-iv |0 a-i^t.ng Co^pufcit and £jp& tkuu uje^i ■ ■ A " 

FOR THE COMPUKlT - Au#mt>aff |dtOi EUJQ 
GAME PACK 5 11 FoiifGimftCLH 2> fw Cimft f* 00 U ?hw<u^«* :^ d.OP 

SuOK Soaca l^adf'l i«»0 MM C hoqu^rt 000 »*a*B'rT< CRx ■ C3 « 
taie 1or C&m&uti.l Q9 50 *0 1#"* E ipar^oi« Jy*npr* Cab* CI » A* P-<« T i ,t .r . i ■ 



CENTRONICS 737 
DOT MATRIX 
PRINTER 



CASIO VL TONE 



roNE^JV 



£31.25 



AT 



I I I I I I I I ID 

II III 11 111 



ti'-a a nwi aind ol mus^a* ini[rurr»n[ A c^mpuihr eonifqpllrjd 
I *yn-th*iia*r thai hfllps you creaia, p*»v and a/range compoai ■ 
Tic*** ih»t normtiy t«A* vwi f^ ^uucal tfainkng. 




WE ARE NOW STOCKING THE 

| APPLE II AT REDUCED PRICES 

AUTOSTART 
EURO PLUS 

48K 

£599 

+ VAT 

Oottinti Startvd APPLE II k lastef , smaller, and more 
EMhMftu! Ihlti Hi pfrd^n44t!| And W% nv0fa f jn 10 VM 100 
occau*c of b«aim leaiurras Mo 
* BASIC Th* Lanoua^Cr |hM Ma*44 Pl00>VMlhnd; Fun 

#K*9h Roso'utiq^ GPfor>icii tin a 54.000 Put f \[ Ak^I tut 
Fmalv Dtuaed Ofplrjri t Sound Caootmn^ thai Br-inos 
Program^ to t >i* • Hand ConuoH. Ioj Gantea- a^yt Oihf' 
Humatu Sntju; AOb-VjI^ns f>miMiuJ MffflATy Clpflcfv "- 
48X Hyi<r» 01 RAM SJK 5^« Of ftOW JV B^-Sv&rayn Pfir 
iamanc£ in a $mal Paci-aojc- • E^ni AEcnsw £*oartvori 
SkJlt io Kl ii>o ^itm Qn&t W-1^ Tnju* Notdf 

You don,'i need 1p bo an * apfrl iofn|Ov APPLE II Ie if a 
conipteli. r*jdv to Jun cofiipufaf Juu fowwrf it to a wctao 
ifirKwiT a4*d viaft itftmti. p'Ogrjma |p« nwEiny yix^r WMBj rh- 
1-r-n /Jay fOuM Irnd th*| rt» fylonjl mf.nyjlsftg*o yOu OT414 1 
your o*n p*rMna» proOaofn torvar 




ACORN ATOM 

UNIQUE IK CONCEPT - 
THE HOME COMPUTER 
THAT CHOWS AS YOU DO 

Fullr Afc^r.,:.:--.: £149 ■ vaT 



5p*ifia4 fHityrpi indwda • Fuh Snad Kiyboaid • 
Asaarablar arid Bas-c • Top Qualify -Moulded Caw * Hhgh 
RosokJtwn Colour C^aphici • «05 Mcroproctaior 



THE VIDEO GENIE SYSTEM 



EG3000 
Series 




t*" ^^tlASIC inflOW •Fu«»TBS'flOt*rt M 

'-.v...-, '.■■•• 

nm of wltvyam *1r»idy avi«lahl« • S** co^t*in*jd PSU 
UMF mgdulalOr. pnd rj^rr'Jn 5-inCilv plugs k*H0 V-dfrO 
mo™ior or UHF TV »Fufl asEMn*to« Io 4*fkf and pftftf* 
■ AfjMlutalv c^molati mil til »n?s mam* p*,^ 

the- V-d«o Cffrrnu •« ji Compfcft'te COrrtpu^ Sy!i , !-?n-! i . • 

orav Connjcten eo a dom«»t< «$ una TV w: i :• ' - 

OpatfKnat; O* M EGOuiEOO a ¥*O*0 rTwuiOf -van Emi c n 
10 provide Eh* be*i qua^ty d4pi*¥ %1 L^y rvO*w '--■■ %■. =■ 
kfrvboard:. nvfiich fiiium 8 10 *fy rertov* r Sucp^-Td ^1" 
th* Ttflowmp acftudnat .« #eA5lC rJtjmonivatio^ tipe 
•■'.-•ddo laad *$anorhd cauttnr toad. #Ua#*¥ n 

*BASBC m^r^jjl B«9inn#tf^ prciyrjm.-inij man .« A' r * 
ui£«ul pjoo,!^>^s ii ■ rhe BASIC CDrnputcr lan^uapi tOvniorf 



V 




HITACHI 

PROFESSIONAL 

MONITORS 



9" - £129 
12'' - J>99 



£99.95 
£149 



So*d iiaia CKc-yfiry „i.^ a- >C *nd iAcon 
i-j-vtiiCKi amui«t b*^ *vhpt>:«.tv » M» Nn^i Noriionlarf 
i*«oly(ion Mo-ifoniai <aaoiui^ri . , ■ ^t >n«n> 4 

#ch*wd in D^BuiO «#nior * Sum ptCfur* €^«f- played 
back pffCiuraii el VTN otfi W d4p4awd * si-out fitcirmg 
* Loocring vfd*jo Input VMco tj._: ia- be looovd ihrougb' 
with bunin b7iAanal«n vA^ti • Ea1*>m*l aytic opaaar- 
H«n avaHaUa aa OlfflH>h fo^ U aftd C TvpOtJ * Compact 
conalriK liofi T *fQ fnonmio*t a** movnqblff i*d* b> *»d* m a 
sijndarj 11 ncn *«i. 




£79.90 







O^'iv^fy 'Si Added an cost PttaiK rn^kr* chHH)ujo$- Ond poilol coders payable to COMPSHOP LTD., or phone VOU* 0'dtr 
quonrvcj BARCLAY CARD ACCESS. DINERS CLUB or AMERICAN EXPRESS mjmbei 

f ^ L TI T J J>] 4 ; 1 ^ ^ ■ ' I il ^TT^aUlf credit facilities arranged 

14 Station Road, New Barr^E. Hertfordshire. ENS 1QW r'toje ro AAew ffa/ne? 5/? Station 
Telfiphonc: 01 441 2922 :Salesl 01 449 5596 Tele*; 296755 TELCOM G 
OPEN (BARNETr - 1(Tim > 7pm - Monday to Saturday 



trjr applit^lior - 



Pj'SOfii/ Computair Slops' 



NEW WEST END SHOWROOM: 



311 Edgware FfQ/jd, London W2 Teleph&ne: 01 262 0387 
OPEN (LONDON) - 10am - 6pm - Monday to Saturday 

A IRELAND: 14 Hhrb*rt Stri*<. OuWifi 2, T*taph<hn* tjublnn «M1B6 

ak. COMP5HOP US A, ii«l Eats Eoifroa^. Sani* Ana Cafatoin**. Z* Coda 97706 



OPEN 24 hrs. 7 days a mum* 
01449 65% ' 




■* "T- * ""I 



6 YOUR COMPUTE ft, DECEMBER 1981 



What would Idowithacomputer? 




■ J »«4 J L V J h.m * nk i tUP rm n 



kV, K 4 M |i- , * .- ^n.7Hh Ate Jhc***? ^piMi^'h} 
IMinrc-* i«W *fhrfccn«^fjrtn.frityiiitlftiiiiPirl 



Ai jmi *K€ J >aih» ft* 1 1 1 >*? 






You'll be surprised how much you can do 
with a personal computer and even more surprise J 
at how little it costs. 

We made it our business to find not only the best 
value-for-money computer on the market, but a Iso the 
best books to enable you to progress from a beginner 
to an advanced user. And W,H. Smith is the only 
retail chain where you can buy the incredible ZX81 

The Sinclair ZX8J is a masterpiece of design. 
Which is why it can carry out programs yould 
normally expect from more expensive computers. 

Although the ^X8l is fast and powerful, 
it's also simple to use. Within hours you can learn to run pro- 
grams and within a week you could be writing your own 
complex programs. All you need is your own TV 
fany model thamecetves BBC2) and a cassette 
player when using pre-programmed cassettes. 
And W.i f. Sm ith have a range available from 
£3.95 each. 

So lake your first steps in computing at 
W.H, Smith and make your life easier to run. 



The first personal computer 
that only, 
adds up to 

£6995 





Prices correct ur lime or going 10 prcs*. 

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- Ncwttsae-pficimoAWw-'Nort-hiTipflfi «"fen*:ch NafltMJwn Liwoht Noci:-raiumVitiont*-UfFiF-pnn »r.i.rii r.-KT&Brwfh Fltrnwipi ftiflirfws p»t Fwremhun Fysra* %*Jt- Atcbmvfti 
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.-j Wgh-ethuWW t^weC*** Woototfi Wm*tur Worthy ■ w^hini ■ Yiwfc 



YOUR COMPUTE* , DECEM&Efl 19&1 7 



imrnmmTim^^ 




ingenious! 



. . . thats the only word to really 
describe the superb Genie 
microcomputer system, the 
home computer which is 
compatible with the TRS 80, and 
ideal for all micro - enthusiast s 1 
especially the committed 
hobbyist. 

Genie has now beer* upgraded 
to Genie 1. incorporating all of 
the original excellent features, 
but with the addition of; 

• Extended BASIC, including 
RENUMBER and SCREEN PRINT. 

• Full upper and lower case, 
flashing cursor and auto-repeat 
on all keys, 

• An internal SOUND UNIX to 
add a new dimension to your 
own programs. 

• A MACHINE LANGUAGE 
MONITOR, with Display modify 



enter and execute (with break 
points) facilities. 
Genie I has all of this, plus the 
built-in cassette deck, 16K RAM. 
12K ROM with BASIC interpreter, 
full-size keyboard h an extremely 
wide range of new and up-dated 
peripherals, and literally 1000s of 
pre-recorded programmes 
available. 

Yet, almost unbelievably, the 
price of Geni^ I is even lower 
than that of the original Genie! 

Ingenious for business 

The Genie II is a major 
breakthrough for small business 
computers. Harnessing all the 
advantages of Genie l f including 
low price, Genie II adapts 
perfectly to commercial functions 
with the following features: 



« Numeric keyboard 
' Four usable, definable 
function keys 
i Extension to BASIC 

> Basic business 
commands 

> Fully expandable with the same 
periperals 





8 YOUf* COMPUTER. DECEMBER lSBT 



^-J\& 



New * , , 18" Monitor. 

There is now a choice of 2. 12 " monitors 
with the Genie I system, allowing a 
clear, easy to read image, and no 
interference with your domestic T.V, 
viewing. The new EG 101 comes with an 
updated, green phospher tube. 



New!*.. Expander Box. 

An updated Expansion Box 

(EG 3014) is a major feature of 

the new Genie I system, and 

unleashes all its possibilities, 

allowing for up to 4 disk drives with 

optional double density. It connects to a printer, or RS232 interface 

or S100 cards, There is 16k RAM fitted and it has a new low price! 



^ 



"//> 






New! . . . Parallel Printer 
Interface. 

Enables you ro connect the printer 
directly into the Genie computer 
without using the expansion box 



New! . . . Printer 

The EG 602 printer can be 
connected to the Genie either 
through the expander, or 
directly into the computer using 
the Parallel printer interface. It is 
a compact unit, with an 80 
column, 5x7 matrix printout, 
operating quietly and efficiently 
at 30 characters per second 



Disk Drive. 



4 



As well as the obvious advantage of mass 
storage, the addition of the disk system to 
the Genie means much faster access to 
other languages and full random access 
file handling, Up to 4 of these 40 track 
drives can be used on a system. 



Newt . . i Double Density Adaptor 

Doubles the borage capacity of your disk 
drive by allowing it to work double - 
density. 



*«* Mr 3> 



,- 



IB SPECIAL TECHNICAL GENIE 

HOT - LINE ON 0629 4995 



For full details and demonstration of Genie I, Genie II of advice on any aspect of Ihe 
system, either call in to your local dealer, or wriie directly to the sole importers at the 
address below, 



Genie I and II approved dealers 

AVON Kii.TPiljta.HiEh 022 5 3 34&S'»- 31*70* BEDFORD 
C<jinpjEdp;i. LwgfolopflLiiiiid &52S 37fift&3 C&mfiOIYS, 
a^rir.Tii 023:4 7-H 749 BERKSHIRE PC P.Readuig. 0134 
5|.*243 BIRMINGHAM ! M jskys M L c(£dig.ili: 
3-.rrr.rn.rari ?2]-£J2$3tf3 Wud EtatfxOnLCi, 
BHmirghun M!h5S4O708 BRISTOL I jskyi 
Mrcrodk^.Bnilol 0273 2042 i DUCKTNGH AM EH SHE 
: ■■ ■ i -■ A - ■■ • ""^i ifpe r - j ;.)■ iU "-' | r I i : If 

ItfafJfcCt Cor^pcr.cji:* ^nvershun G24B322M7 
CAMBRIDGESHIRE C inti:dgc Mlced Computer*. 
Carr.brjdge 0223 .11 |{&l CHESHIRE H twirl 
HiirilOiiC j, ftlfcCClWftild' Of 25 212 20 Mid Suites 
Ccunpatei Cirri*? Cr*"*p L*iky*MwTo4iflii»l,c;hir&:L^ 
03 4 i .j ] 7C ■ T CU MB PI A Kenditt Computer C*r4i *. 
Vr-i' D$3tH*ai' S:nti:ekM ■ - -■*!..?<- :. r - 
37 iH PEREYSHIRE Xayi Electronic*. Ctoiteriirid 
02H- 31 HE T C route v Cteitcrlwld. 0244 IISttH 
DORSET Kirdfwd Conp-dicf*. Biandford Forum <i3&^ 
51737 Piri(H^r*E^c1nri-P«i4o,a3«74& £ ,&& ESSEX 
ET-.prji-e Colchcrtcr. #£ DC If 59?£ Crrr.piislc:!.! P.crHard 
070F7 51&G& [r.!ni*b Chi-]mif«4 fift} 35733 I Micro 
Computer Sflrncti Clarion or. S^i. OK 5 5 J 30 JP C5SC 
Itfofd.01-551 33 44 GLOUCESTERSHIRE M PI. 
Cattipdtei* Chiller I d.r PL-LrieSyitenj; 

CreherJum. E-242 <55I£E-l- Compirfer 53i act C£uriler.p*rn 
0H2 5*424:1 Zdi C=.rrpj1*Ti >!o™tr.,:i5P M5J**Z*4* 
HE RTrORD SH ERE Vh pI p A - cuHxt iViHard Q923 

WiJCnid Etapttpn.L-3 Wizard. I>M 3 4056R. 17774 
QT#k Syiltmi SK-VoTnqr. Oil 33 £5 3fifl CompSrpp Ni-w 
ajiri-H :]-41L2yZZ KENTMj":ii CamputDTSyslrrns 
fi-eci eaJi-ish. I L ■ 6p"p 7 UV , r pE I B'jtihrtt Sysierm 
Hernpi1#*d. GG3S 362652 Tin? Cumputr Rbnni 
fljfLbjjd-g* WelLi. M92 4 L€4 5 SMC MBProc-DmpuS&rfi, 
GriveSprd D47fl 553] J Swante; 1 E^clioniri 5-wantay. 
03.2.2 ti 55 1 LAN C ASUIRX Lm&jx Wtcrpdigil*] 
LiTcTpni-: DS: 227 2515 MigSi'v- MictP . BurnLcy G2I2 
5B7SB Lniucomci Blackpool 0Z53 275!*D Harder 
Mjctoiywefhs, BlackpooL D2&3 275°^ Msc:c Ciiip SH.op. 
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iB4b! Cyrf.putcJL'iI LeJ^h .B342GDS7JC LdnHyi 
Microd^UPt^Oh.^T^ 53261 LtlCESTERSKlRE 
Etay £lrc1l Qfllc I Lp-l'p tut 0533- 87 1 S2Z Af d*fi DiFa 

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M5CTO*y«*m*.ECa.*l*5«^7: * IXJNDONfNORTHI 
lAdlO%lC4t.KVf$ l Q]^4?i74Cri ; : : rjc;r^*rr 

Horf, 014«£ 0837 ChiOffMtotiic Etacifonic* Mi9,«t.SA& 

5433 Wj^onMK^Kh^mft.fli 407 H 57/2230 CCKAp 
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NSasheiirig Wr- 01 2Jf. ?3i4 LONDON £SOUTH|Ui9evi 
M&CHdi4i:al Kihqu&ft, 01 ■ 5-46 1271 MANCHESTER 
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2efr9£. a«3tnciti . EtateftUTL 03*2 24 1 
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»STofr7a3.Ml£loakitin vi a;5yi1irni> Witk4n#f.DWi 
73143. SCOTLAND C« rr.-|ruict ahd Crupi St AnAewc 
iJfJ4 M»* UfkriMEfiodtuNbiE Liriu W r, .Mi -SK 
ZBI4 Scolbytt Compvlir* Lti^bm^ «5-J« 10Q5- 
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C r-.n-.j: i: I ,-.r? G4jm«« -i.Jvi, L I, £.,i. ; n CTvflJc 
tditiliut^h. 031-3 32 5277 SHROrSHtRE T-ift an 
LI-ji 11 ii-Jri NewpcH. JKS2 S:2] 34 SOUTH A«rco 
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H i El mg p. 04^4 4 37475. &i:n*f if i^ht pti ^273 ftfi*Z * 
SOUTH WEST CM iM ps? Lid ftrftQrtdV C*7S2 27^000 
Diskwi«Lid.C*LLpgt(Hi 557^5^79-3 EjedTOciirp 
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■iVlvvJt&ft. OSi ZfkS J43J. SUrrOLK R^Uuaie Cowpirtet a 
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Chesterfield Road, Matlock, Derbyshire DE4 5LE 
Telephone: 0629 4995. Telex: 377482 Lowlec G. 



YOUR COMPUTER, DECEMBER 1961 3 



The Northern Show that means Business 



/j 



quality audience 
were delighted 



John Bowden, Sales Manager 
Research Machines 



Comments like this were made by 
many exhibitors at the 1981 
Manchester Micro Show - in fact so 
encouraging has been the response 
that two exhibition floors have been 
made available for the 1 982 Show. 

If your organisation has not yet 
confirmed its booking ring the 
Online Exhibition department now. 
They will reserve your space 
awaiting your written confirmation 



Jlf^JVCMgSTS^ 




SWOU/ 



3-5 March 1982 
New Century Hall Manchester 



Online Conferences Ltd., Argyle House. Northwood Hills. HA6 1TS, Middlesex. U.K. 
Phone: North wood (09274) 2821 1 Telex: 923498 



10 YOU* COMPUTE*. DEttMBEfl 1931 



YOUR LETTERS 



ZX-81 CODE 

A fter reading the November issue 
^1 from cover to cover, I Tried lo 
run the programs in iisting 2 of 
Brendan Clancy's informative 
article Ii seems to omit Tour value* 
bet ween addresses J 6586 and 3qd6I, 
and I wo values between addresses 
16686 and 3 6736 

This was my ftrst attempt at 
machine-code programming so I 
took great CM to enter all the values 
and have re-counted the number of 
bytes given in the listing several 
times. Please can you. prim the 
miss ing value*, or e-eil rac where I've 
gone wrong, so thai J can at Last see 
the advantages of machine-code pro- 
graming? 

tftA Gan*r t 

Hampshire. 

■ Before byte number IGBtil 

Insert two lines which should 

read: 

LDHL 16438 33,54,54; crash 

INCEHLf 52 

Just before byte number J 6736 

Lniert: 

JR Z 6 40,6 

Line number 2 in the first Basic 

program should read Line 

number 5. and there should tx A 

tpace bcTWeen the " " in line 20 

in the second Basic prnjjrflm. 



FAULTY CASSETTE 

The art k fee by Eric Decsofl on 
ZX programs in the October 
issue was excel lenL Et arrived in time 
to nop me from pulling the 
remaining grey hairs From my head, 
I had repeatedly tried to load my 
cassette and had tried everything, 
including prayer, without success, 
The article reassured me and I have 
subsequently returned the cassette fo 
Sinclair Research for exchange. 

r should add that the cassette sent 
was a free cassette issued to calm my 
nerves because t had waited since 
July II for a RAM. 1 have not as yet 
received two cassettes ordered at the 
same time. What a pity that such an 
excellent machine as the ZX-£1 
seems to be marred by such inaoV 
quale software and after-sales 
service, T hate to ihlnk what use ihe 
cjisxttcs will be when they 
eventually arrive. 

D B Orptf^ 

Bmbrwk, 

Linmfn. 



RAM ALTERNATIVE 

In the October issue of Ymr 
9 Computer, P C Jowsey indicated 
in Response Iramt that the circuit 
diagram supplied with the kit 
version of the ZX-81 suggested the 



use ofa 481© 2K RAM instead of the 
I K RAM supplied. 

1 have carried out this modifica- 
tion but using; a \$02 which is an 
updated 2^ pin version of the 4816, 
It is p incompatible with the 4118 
escept that pin 19 must go to the 
A 10 tail — as for the 4816. 

The 4064 could be fitted to replace 
either of the del ices mentioned — 
this will give 8K of RAM Ail these 
RAM* are available in the Mustek 
By t e wide series and can be fitted 
without any serious modifications to 
the prinlcd-cireuit board. 

1 am a newcomer to the Sinclair 
ZX-8J which I have just finished 
constructing I read with interest 
that some users have had problems 
recording on cassettes from the 
ZX83 

Some very cheap cassette 
machines have an integration 
capacitor across the speaker or 
earphone socket. Mine had one of 
O.Q6o>Fand I found that it upset the 
replay inra the computer. Removal 
of this capacitor completely solved 
the problem. It" you are lucky 
enough to have a circuit diagram, 
cheek to see if your recorder has this 
capacitor. 

I found that cheap cassettes could 
nor be used. Their oxide is such that 
they do not saturate properly, and 
recording digital information 
becomes impossible . Medium- 
quality casseires such as BASF SL or 
similar arc suitable. 

I hope this helps others who may 
have problems with ihe ZX-8L — it 
;s possible that the problems do not 
lie within the computer but with the 
cassette recorder. 

Stuart Stirling, 



ZX 81 CONTACTS 

■ have found the solution to fitting 
f the ZX-B1 RAM pack securely. 
The main problem is that the RAM 
pack wobbles when nudged even 
slightly, which is due to poor 
contacts and results in total data loss. 

To cure the problem permanent ly> 
you must first remove the ZX circuit 
board from the casing and then plug 
in a soldering iron, When the iron is 
hoi. apply small quantities of so-lder 
to the strips of solder already present 
on ihe hoard. This should be done 
on both sides of the output port, so 
thai the RAM pack fits much more 
lightly. 

1 also noticed, in your October 
edition, that Eric Deeson had 
loading problems with some of the 
software he was reviewing. He 
Names software-recording quality, 
bul I am reasonably sure this is not 
the cause. The problems are more 
likely caused by cassette-player 
incompatibility. 

I have found that speeds and tones 
vary according to the cassette players 



used — I have eight of them. The 
simplest cure for this is not to send 
the software back to the suppliers 
but to borrow someone else** player 
and try with thai. When the program 
is loaded into the computer, save ii 
again on your own cassette player. 

J&H Software, 
Littwurwc, 

Wa-rwkkskirt. 



SCOPE TEST 

jH ftet * Look ihrouph the Your 
^% Computer survey of program and 
tape standards in the October issue » 1 
think it is worth mentioning thai an 
oscilloscope ts eatiremeh j^l-IuI 
when making or resting ZX-81 tapes. 

So far, we have only examined our 
own tapes — made in the course of 
developing a reliable mass-duplica- 
lii-ii: ^vsxem. 

The oscilloscope is probably the 
best tool fox distinguishing between 
perfect tapes, those that will load 
with a tail wind and some luck and 
those not worth spending time on. 
The only problems that the oscillo- 
scope wilt not bring to light quickly 



^ VH .rrr 

WKwfwHh WtenltariTY 



are those which only affect part of 
the tapct c.| r , dropouts and bad 
patches. These can be very largely 
avoided in production by using 
good-quality tape. 

All our batches of tapes are tested 
by sampling. It" i few sampler load 
impeccably, and the wave- form is 
near perfect* we accept the batch. If 
anything suspicious is found* we test 
part of each tape for a few seconds 
on the oscilloscope, 

Mikr Salem, 
Hifdrrbray Ltd, 



"LIFE" ON 16K 

9 X-s] owners who have tried to 
£ run Sinclair*;* Life program with 
a 16K RAM pack filled will know 
that ihe system crashes — albeit 
gracefully. The following procedure 
permits the program to run with 
I6K, Load the program and enter 
these three lines: 

900 FOR N = 16666 TO 

f&550 STEP -1 
910 POKE IN + 2K PEEK N 

en met n 

Then tvpe: 

GO 1Q 900 
Amend line 700 to 

700 LETC-USR 18572 

Lines 500 to 540 inclusive arc now 
redundant and lines 900 to 920 
should be deleted. Save the program 
before running. 

This procedure works because the 
original program ran with a page 
widrh of 16 characters k whereas the 
loK RAM creates a 32-character 



display. The two additional memory 
locations created by opening the 
machine code at the right place 
ami -jut the shift left instruction, and 
effectively multiply the page width 
by two, 

Martin Buckley, 
Southampton- 

SKETCH SUCCESS 

M agree whole-heartedly with the 
• opinion G A Bnbkei expressed m 
?!:<.■ ,\ueuht-Scp'cn:bci i^-m^ aboiN 
Sinclair cassettes Admittedly it 
requires very little work to make 
them run smoothly, but why leave it 
to the poor purchaser — iuteh- the)' 
could have been altered before 
nLcttc? 1 was undoubtedly unlucky 
— 1 bought cassettes I and 4 and 
have had to return number 4 because 
of errors. 

Eric Deeson's Sketch Pad program 
in the same issue proved a great 
success with my children, but they 
kept entering too few or too many 
characters, which of course termi- 
nates the program. This can be 
avoided by adding between lines ° 
and 10 or 90 and LLU). 
95 IF LEN AS< >3 THEN GO TO 60 
Gilltan Turner, 
St Nfots k 
Gambridgetkire. 



VIC OR ATOM? 

/'am at present considering buying 
a microcomputer. I read the 
September issue of VW Omput^r 
and found it very informative. 
However^ having joined the local 
computer Jub - something 1 would 
advise anyone in a similar position 10 
do — 1 have had a chance to use 
several home computers and 1 am 
forced ro disagree with your views 
on the Vic. 

At the price of about £300 for the 
Vic-20, the Super ^pander Can- 
ridge and the cassette recorder t t 
cannot see that it is good value when 
compared to the expanded Acorn 
Atom, This machine offers twice the 
screen capacity and if the colour card 
is used, it is mere than a match for 
the Vtc graphics. 

Admittedly j the Aeon? has a non- 
standard Basic, but once you become 
accustomed ro it, aided by the 
excellent manual, it is easier to 
understand than the Pet version. 
Added to this is the fact thai ihe 
Atom comes as standard equipped 
with an assembler, rather than the 
Vic's clumsy Peek and Poke — 
surely a big point in its favour. 

In short t fee! that this British 
competition is more than a match for 
imported machines. 1 would advise 
anyone wanting a computer to buy 
British — not only out of patriotism 
but for value for money. 



SuTTty- 



VOUW COMPUTER. DECEMBER I96T 11 



NEWS 



Co-op to help 
U.K. clubs 

Cooperative Retail Services is to 
create a network of home-computer 
clubs for l-.^ customers, members and 
stair" Ii has Ioiik been ilie practice of 
the Go-opcr ati vt movtme n i to assign 
part of its profits to financing 
educational, cultural and leisurc- 
tjote scheme*. In the past, the 
money has been spent on a wide 
range of activities including choir 5% 
youth groups and classes. 

The Cooperative Societies' 
national member relations officer^ 
Frank Dent, says that he sees home 
computing as possibly the biggest 
leisure growth area which could 
soon rival photography. ifc In the Co- 
ops we have always tried to respond 
to new needs. I am convinced thai 
there must be many Thousands of 
people fust waiting 10 join home- 
computer clubs". 

To si an such a club* contact Frank 
Dent* CRS Ud, 29 Danizic Street,* 
Manchester M4 4BA. 

Upgrade ZX-81 
memory to 48K 

OWNERS OF either the Sinclair ZX-80 
Of ZX-S1 microcomputers axe con- 
siamly frust rated by the shortage of 
use ^memory available for their 
machines. The meagre amounts of 
RAM available with the basic 
machines is enough for a very simple 
program but for one of any degree of 
sophistication, the low-capacity 
memory is prohibitive. 

Many ZX fans find the greed for 
memory satisfied by the 16K RAM 
packs which wobble about on the 
rear connector. Ycr for the more 
avaricious memory user* even a 
generous I6K may not be enough. 
For [how h Memotech has introduced 
a new 4flK memory extension. 

The Mernolech memory-estension 
board will allow ihe ZX-fll to run 
48K Basic programs which can 
include up to )6K of assembly code. 
The memory it available in either a 
ready- bu ill form or, for ihe more 
adventurous, a kit is available- 
Unlike the 16K RAM pack, the 4SK 
memory extension is complete with a 
power supply which services the 
computer as well as the memory 
extension. 

The memory extension resides in a 
case on which the j£icfocompuicr 
sits. It has a fuliy-buftercd control- 
data-address bus with a printed- 
circuit board 40-way header plug. 

The memory is conligured in such 
a way [hat there is a 16K "gap" 
between 16K and 32K for assembly 
programming. Top of memory can 
then be set at any point up to 64K„ 

The ZX memory expansion costs 
£129 plus VAT built, or £109 plus 
VAT for the kit. For rhe Nascom 2 
the memory expansion costs £35 
plus VAX Memotech: 0865 SI 3356. 



Sinclair seals Japan deal 




ClIVB SINCLAIR has pood reason to 
look pleased with himself. The two 
gentlemen with him are British 
representatives of Mitsui, the giant 
Japanese trading company > who are 
about to begin marketing the 
Sinclair ZX-S1 microcomputer in 
Japan, 

M Qhtaki, left, assistant general 
manager at the London branch of 
the Mitsui organisation and Hiroshi 
Sh im L7-u , r ig ht h r he manager of M iTSui 
computers, told Y$ur Compuftr that 
Miisui would be selling [he 
machines in Japan using the same 
mail-order techniques Clive Sinclair 
pioneered in the U.K. 

11 We will retain the English- 
language keyboard — the difference 
in languages will not be important in 
the market where we are selling. We 
regard the ZX-81 as an educational 
toy". 

Shimizu is the man responsible 

This is the ZX-87 Print *n* Rotter 
Jotter from 3uil&r f Currie end 
Hoot, It is a useful aid for 
anyone interested in exploiting 
the graphics capabilities Of the 
Sinclair microcomputers to the 
full. Consisting of & tear-off pad 
of 700 leaves, the Jotter has each 
page* printed with a ZX print gnd 
and a ZXplot grid. Each grid is 
fuNv numbered antf clearly 
definite. The pad measures 
7t.7Sin, by 8.25in. - the 
standard A4 size. On The print 
grid each of the 704 character 
positions are shown end 
numbered. The plot grid has M 
2,816 pixel co-ordinates. The 
price of the ZX-W/St Print V 
Hotter Jotter is £3.50 for one 
pad, Wh#n ordering by post, 
second and subsequent puds cost 
£3. 75; if five are ordered, a free 
ZX Print V Plotter Film i$ yours. 
The fifm costs £2 if bought 
separately. Discounts on target 
quantities ar& offered to clubs 
and user groups* Th# retailer of 
the Jotter - Sutter, Cutrie and 
Hook, 1$ Borough High Street, 
London SEI — is planning to 
extend the scope of the Joners 
to cover other papular micro- 
computers. Butler, Currieand 
Hook can be contacted by 
tefephons on 01-403 6644 



for negotiating ihe deal which has 
opened up the world's second 
biggest mif cocomputer market I o the 
world's best-selling microcomputer. 

The announcement was made 
simultaneously in London and 
Tokyo, and is of a great deal of 
importance as Mitsui is responsible 
for 10 percent of all imports to Japan 
— everything from British Ley laud 
car$ to Scotch whisky, Mitsui 
expresses a wish to import more 
foods to the land of the rising sun 
and in fact extended an open invita- 
tion; to Bnnsh innovators to contact 
ihe company to sell any high-tech- 
nolopy product 

Clivc Sinclair *aid rrur he 
originally believed the Japanese 
market to be too dtfftcuEc to enter. 
However^ with the expertise and 
resources of one of the world's 
largest trading companies behind 
him, he said he wa* confident, 



Payroll geared 
to small firm 

A I&I4J i hum payroll program 
together with slep-by^tep instroo 
lions, which runs on the ZX-81 with 
l&K RAM pack and printer, will 
perform all rhe jraymcni and 
deduction rakttistiotH and keep the 
records for a small exttrtpicrj with 50 
or fewer employees. 

The program can also cope wnh 
bonuses and any ex visional pay* 
ments which need to be made Ic can 
also gross a neti payment There is a 
program-reptactmenT service in case 
of any sax changes Contact 
Hildcrbray Lid, 8-10 Parkway, 
London NWl 7AA Telephone 
01 -«5 1059, 

Learning Basic 
in the lab 

S inch aim Research baa developed a 
hands-on ZX learning laboratory to 
enable users to learn programming 
at the machine Developed by 
Sinclair to meet popular demand j 
the laboratory comprises eight 
cassettes and a 160-pagc manual. 
The 20 programs twh denuanslratc 
an aspect of ZX--81 programming. 
These aspects are spread over the 
first six cassettes — the last two are 
left blank for the u*er to practice 
with. 

The laboratory is available from 
Sinclair Research, 6 Kinps Parade, 
Omhridge. CB2 ISN, and costs 
£HMH 




12 ¥0118 COMPUTE*, DECEMBER 1961 



NEWS 



Schools enjoy 
special price 

MOMI TMAK 2,300 secondary schools 

have opted For the Sinclair ZX-6I- 
Tht machines were sold to the 
schools under a special low-price 
scheme which was run earlier this 
year by Sinclair in conjunction with 
educational distributors Griffin and 
George. The scheme was Qivc 
Sinclair's personal bid to widen the 
choice of microcomputer cquipmcnl 
available to schools. 

The Government-assisted scheme 
restricts the choice of machines tc 
cither the Research Machines 3S0-Z 
or the new BBC computer from 
Acorn, Give Sinclair commented 
that Although wt welcome ihe 
Government's irhiarive s we felt char 
ii did not fully account for the erata 
of all schools. We believe thai the 
success of our scheme vindicates our 
approach as both practical and 
economic". 



Vic extras that add power 



A wide kxxm of Commodore* 
approved peripherals for use with 
the new CBM Vic 20 micro- 
computer has betn released by Slack 
Computer Services. The peripherals 
give rhe Vic many of those facilities 
associated with larger or more 
expensive computers. Judging by the 
response Stack has already received* 
these products are destined to be 
very popular. 

The most obvious add-on to any 
small microcomputer system — after 
the tape recorder — is extra memory. 
RAM is atwavs at a premium inside 
any microcomputer^ especially those 
which do nor provide much as 
standard The J*K of RAM pro- 
vided with the Basic machine should 
be enough ro keep most happy for a 
mii!-r!j ur. two, .bynwn the user uil] 
want more. 

Stack markers a 3K memory add- 
on for £39 which has the advantage 
of moving Basic ro the same memory 






1 .-* 


i ~f— — 




El 


3 ■ 


m 





The first ZX Microfatr was such an overwhelming success that people 
queued all the way around London's Central Hall, Westminster, for hours 
in the pouring win, Considerably more then 5,000 ZX enthusiasts 
attended and the opening hour 5 towi .'■■■■ b€ extended so that everyone 
could have a chance to see the exhibits, The 50 stands in the packed haif 
reported extreme/y brisk business, with some stands recording sales watt 
into four figures. Because of (he response, organiser Mike Johnston is 
planning & second fair to be held ot Central Hall, Westminster, on 
Saturday January 30. This time, to cope with the rush, the doors will 
be open from W. 30 am untifS. 30pm. The floor space wiff be doubled to give 
everyone room to breath. Anyone interested in axhioiting should contact 
Mike Johnston - after 7pm, on QI-SQ1 9? 72, 



The Vic joystick from Stack is just cm 

space as on rhe Commodore PeT - 
that means programs written on the 
Per can be transferred. The unir 
plugs into The Vic smd acts as the 
memory port so you do nol lose any 
of the machine's facilities. Another 
Advantage of rhe device is thai il 
offers hiith- resolution graphics. 

There *n? in fact a whole range of 
memory expansions to suit every 
user. They are available in both 
CMOS and NMDS and range in sise 
and price from £1 MO for IK up to 
£184 for 24K. plus a swiichable 3K, 
Another memory product of interest 
is the 19K memory expansion which 
is battery-protected so that programs 
remain even when rhe computer is 
switched off. 

The £25 Vic light pen will work in 
both rhe normal and the high- 
resolution modes. The pen enabies 
you to interact with the computer 
WLrhoui using the keyboard, 

A CBM Vic can be used as a 
remote terminal to a large main- 
l"u:r.e computer or can control a 
printer or any of a large number of 
other peripherals by the RS-212 
interface. There are two versions, 



Forth reviewed 
for Microtan 

Tangerine is assessing a Forth 
compiler for the Microtan. Its 
release will most likely coincide with 
the proposed new disc unit which is 
also under development. Forth is a 
Structured programming Hanftuage 
ideally suited to microprocessors and 
has been hailed by many as the 
Language of the future, 

Unlike Comal or Pascal * Forth 
bean little resemblance to any form 
of Basic. One of its key features is 
the manner in which users can 
define their own key- words. 

Tangerine has withdrawn the 
discount facilities enjoyed by the 
Tangerine Users' Group, commonly 
known as TUG- To continue to 
provide users with some degree of 
after -sales support of one kind or 
another, the new customer-support 
engineer Paul Kaufman Will edit an 
owners' newsletter Tht TtQ&jft 
Gazttie. Free copies of the first issue 
will be sent to all Tangerine users, 



Noise-generation board 
fills the sound slot 



R F.DUKDAKT mai n Frame comput er 
designers do not die or fade away — 
rhey move info micros. At least that 
is what happened to some of those 
made redundant by ICL, They 
formed Bulldog Video Ltd* a com- 
pany which will design and market 
products for The hobby and small- 
business microcomputer owner. 

The first product to be released 
from the company is a pro- 
grammable sound-generator board 
for the Tangerine microcomputer. It 
is Tangerine- sized, slots into the 
system motherboard and has an on- 
board speaker Ai\d in audio-amplifier 
so that sounds can be produced as 
soon as It has tieen inserted. For the 
perfectionist j three terminal blocks 
arc provided so that it can be 
connected up tn your Bang and 
Olulsen. 

The board is centred on rhe 



General Instrument AY- 3-8910! a 
powerful sound-synthesis chip, The 
sounds produced consist of a 
mixture of three channels^ each with 

an independent tone generator and a 
white-noise generator. The ampli- 
tude of rhe sound can be managed by 
the envelope-corn ro; facility 

Documentation with the board 
explains how various sounds can be 
obtained. Bangs, gunshots, whistling 
bombs and explosions are there in- be 
included in games, Musk creation is 
also possible. 

The sound board is programmed 
via a set of H registers which can bt 
accessed from Basic* assembler or 
the Tanbug M instruction sei. The 
board has full documentation, 
including the GI data manual and 
the Bulldog a manual which 
contains sections on how to start, 
how to program the beast, a guide to 



* n&W range of peripherals. 

otic at £17.25 and ihe full impte- 
nidation of the standard interface 

«I £49, 

utliei peripherals include joy- 

lj rwo of which can be used if 

the multiplexor is used, an adaptor 

cable, a switchabk ROM unit and a 

toollul ROM. 

Slack Computer Services accepts 
oi ders over the telephone if you have 
a credit card, 051-^33 «1 I. How- 
ever most of the peripherals will be 
available from your local dealer. 

High-resolution 
on Tangerines 

HiGH-RFSOJ.iiTroN graphics oT 
2^6-by 256 definition arc now a 
reality Tor Microtan users. The 
programmable graphic generator, 
developed by the Tangerine Users 1 
Group, follows in the footsteps of 
the EFRQM programme r and also 
offers a reverse -video ASCII 
character set. 

For more details of these products^ 
com act the Tangerine Users' Group 
on 0202 294393. 




The sound-generator Qox, 
building up a sound, notes on the 
physic* of sound, a list of fre- 
quencies and how to obtain them 
and a now on installing external 
speakers, 

[\-.i? IkuiJ .,1m-. conuuns two 
independent eighi-bit inputioutpui 
ports which can be used for control 
purposes. A second sound-producing 
chip can he added so that* for 
efciiflp!e+ two Chips Could sin^ in 
harmony. 

The Bulldog video sound-gen- 
erator board costs £44.85, or £56.35 
with two sound chips; both prices 
include VAT, Bulldog Video is at 52 
Nash Square, Birmingham- Tele- 
phone 0299-266143. 



YOUH COMPUTER MC€MfiER i$Gl 13 



THE 

COMPLETE SINCLAIR ZX81 

BASIC COURSE 



At las!, a comprehensive text (or your Sinclair ZX 8 1 ! 
The complete BASIC Course is a manual which will 
immediately become an mdispensibie worfcot 
reference for all your ZX 81 programming. 

Whether you have never dom? any programming of 
whether you are an experienced microcomputer 
user, (he Complete BASIC Course win provide itself 
lo you as an invaluable and 

The Complete BASIC Course is designed to teach 
you lo write and develop BASIC programs lor rhe 
Sinclair ZX 81 - no other books or aids are 
necessa/y. All is revealed m our easy step-by-step 
guide with programs and "lest yourself exercises all 
the way through 

As you become more proficient with computing, the 
Complete BASIC Course will continue lo be an 

essential guide, giving you finger tip references. 
numerous advanced programming techniques and 
memory saving devices specifically lor I he Sinclair 
ZX81 

HOW TO WRITE PROGRAMS: 

Even if the idea of writing programs is completely 
mystifying to yau, the CompJete BASIC Course will 
show you jusl how easy it is. In no time you will be 
abte to write and enjoy complex programs for 
whatever use you destre 

Using the proven "TOP-DOWN approach, the 
Complete BASIC Course wrii show you systematic 
and simple ways to write programs. Even 
experienced programmers will benelil From this 
Course, making programs easier \o write and less 
prone to error! 

NUMEROUS EXAMPLES: 
Every concept, every function is fully described rjy 
simple programs I hat you can enter on your Sinclair 
ZXBi m minutes 



The Complete BASIC Course contains over 100 
programs and examples 1 These programs iiiuslraie 
(he use and possibilities of the Sinclair ZX 81 : 

• Home use 

• Financial analysis and planning 

* Educational applications 

• Games 

* Mathematical applications 

* Displays of 'Artificial Intelligence 

EVERY FUNCTION COVERED; 

No matter what your appJicaiion, what your 
confusion about any function, you will find it covered 
in the Complete BASEC Course 

A f ull and detailed discussion is included of even 
traditionally taboo topics such as USR. PEEK and 
POKE 

A handy alphabetical summary section lists ail 
functions, and provides a sftort description and 
example programs of all topics 

A PERMANENT WORK OF REFERENCE: 

The Complete BASIC Course cs an excellent 
reference work for experienced programmers 

(including tips on using special techniques} as well 
as a comprehensive step -by -step guide foe 

complete beginners. 

The Complete BASIC Course has over 240 pages 
filled with information in an attraciive durable ring 
binder - this is a lay-flat work of reference that 
deserves a place next to every Sinclair ZX 8 1 
microcomputer. 



OTHER TITLES AVAILABLE; 

Melbourne House is the worlds leading publisher of 
books and software Tor the Sinclair ZX a i 

The following titles are also available if you wish ro 
expand your horizons: 

BASIC Course Programs on Cassede- 

Alt m ajo r programs in Che BASIC Course are 

a va liable pre - recorded in this set of cassettes This 

is a va i ti able adjunct to the Course, saving you time 

andetion. 

Not Only 30 Programs for the Sinclair ZX Bl : 1 K * 

Not only over 30 programs, from arcade games to 
the final challenging Draugnis playing program, 
which all fit Into the unexpanded IK Sinclair ZX 8 1 
but also notes on how These programs were written 
and special tips' Great value 1 

Machine Language Programming Made Simple 
tor the Sinclair - 

A complete beQihner s guide to the computer s own 
language - Z80 machine language Machine 
language programs enable you to save on memory 
and typically give you programs than run 1 0-30 
times faster than BASIC programs 

Understanding Your ZX B1 ROM - 

A brilliant guide fcr ^ore experienced programmers 
by Dr lan Logan, this book illustrates the Sinclair s 
own operating system and how you can use it. 
Includes special section on how to use machine 
code routines in your BASIC p+ rograms 








iO PROGRAMS 
FOR THE 

SINCLAIR 




WHJR 




#***■■■■ ■■■■**!« *■■■■■■■■■■■■■■■■■■■»■■■■■ 

Order Form: 

Orders ro Melbourne House P u hi i sheet 

131 Trafalgar Road, Greenwich London SElO 

(Correspondence to 

Glebe Collage Station Road. Chcddrngton. Leighion 

Bu«ard.QEDSLU7 7NA) 



-. «i.llllIlJJiUlllll 



NAME;... 

ADDRESS...... rrPP ..™„ fll „™~ 



I IIIWHH IH 






..Postcode... 



i<1i«1HH+r'- 



The, Complete 

Sinclair ZX Si BASIC Course 



g £17.50 
#S 2.50 



Basic Course 
Programs on Cassette 

Not Only 30 Programs/Sinclair 

BtifilK @e§.§§ 



Machine Language 

Programming Made Simple & C 6 S5 

Understanding VourZXfll ROM ®£ * 95 



Postage and Packing 



Remittance enclosed 



r 0.80 




HEWLETT 
PACKARD 




Scientific and technical 

professionals favour 

the HP 85, they are 

being joined by 

increasing numbers of 

business professionals. 

Find out why the HP 85 

is the professional 

microcomputer at your 

nearest Laskys store or 

write to our Mail Order department for more details. 

LA^feCYf is the largest specialist Hi-Fi chain in Europe, in July 1980 they acquired 

Microdigital — an independent, specialist microcomputer store based in Liverpool. 

Since then specialist microcomputer departments have been set up within selected 

Laskys stores under the Microdigital name, these have now been renamed 

Microcomputers at LA^KYf 

The Professional Microcomputer Retailer 
with Outlets Nationwide & Mail Order 




BIRMINGHAM 

1M ■ Corpcro^ri Street., Birmingham. B2 4LP T*l 02 1 -632 6303 
Manager Pefer StoBord 30O vord* from Ekjllfir>g Cennire 

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&flwft*n Holiday Inn and C A A 

CHESTER 

^Fwm NcrihggH* Strcel Chester, CHl 2BZ Tel 0244 31766? 
Manager. Jewny AshcraJt. Nexl to the Tg**n HqII 

EDINBURGH 

J St Jamef Centre, Edinburgh. EH1 3S« Tel 031 556 2*14 
Monoge* Cdrfi Oropef Eon end of frmees Street. Si Jame* Cefiire 

KINGSTON (Opening «•!, 1982] 

3&40 Eden Street. King irq^.KFl I EP Td 01-546 1271 

Oapoi-re Mom Post OhSce * 



/HICROCOMP UTERS 

LAlKY* 



MANCHESTER 

4 St Maty * Gale, Market Srree* Mancheilcr, M 1 I PX Tel 06 1 -832 6087 
Manager 1«V Jacob* Comer orf E>eofwgq»e 

NOTTINGHAM (Qp«"«9 «ny i9B2j 

1/4 SmrPhy Row, NoMingharr. NG1 2 DO Tel 0602 4151 SO 

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LIVERPOOL 

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LONDON 

42 Tottenham Court Rood London Wl GRD Tel 01 M6 (J845 

Mail Order 

Microdigital Limited, FREf POST [No stamp required), Liverpool L2 2AB 




Commodore's brilliant new 
VIC20 home computer rsat your dealers 
today. Now you can get your hands on 
the world's best home computer, 
we're sure you won't be disappointed. 

Here's a brief reminder of VIC's 
many features : 

A typewriter keyboard with 
graphics. 

5K Memory-expandable to29.5K 
user RAM. 

8 programmable function keys. 

High resolution graphics. 

Music in three voices and three 



octaves, as well as sound \ 

Eight border colours and sixteen 
screen colours. 

Ail in a superbly-designed, 
compact unit with built-in facilities for 
expansion. 

Now you can take a look for 
yourself. And even take VIC home 
tonight 

Czi commodore 

^COMPUTER 

Far more information on the VIC 20, telephone 

or write to: Commodore Information Centre, Baker Street, 

High Wycombe, Bucks, or Tel: Slough 79292. 



COMPUTER CLUB 



For ONE unaccustomed to believing that 
State*tinanced schemes ever do much good, a 
visit to London** Notting Date Technology 
Centre proves that this time a Government 
plan h going to work. 

Some J 8 months ago, Chris Webb estate 
Itshed the Technology Centre at Notting Dale 
:n the back streets of Notting Hill Gate. Many 
K slums hive been replaced in the last few 
years bur the area as a whole remains poor. It 
:s hardly the place where you would expect to 
find z computer centre, sited opposite the Free 
Republic of Frestonia — a group of houses 
■•jjupied by squat Eers a few years ago. 

Four years ago, Webb had been working on 
community projects with 16- and i7*year-oEds 
who were mainly unqualified. No status, no 
>obs, no prospects * poorly housed. He had 
foreseen the Weak prospect of six or seven 
million unemployed by the late eighties. 
Reading research papers, seeing the engineer- 
ing industry contract and computing grow, he 
decided to "dance with the silicon devil". 

With the assistance of interested staff at 
Imperial College, the Institute of Education 
and the Harrow Trust — a local charitable 
organisation — he started putting resources 



Notting Dale 

Technology 
Centre 



An inner-city success story can 

be seen in action in a West 

London workshop where up to 

30 youngsters at a time are 

using the facilities of the 

Centre to build themselves the 

foundations of a career. David 

Pollard reports on this 

Government-funded project 




Work at the centra includes development of aids 

together. £750,000 was raised. A disused 
bakery was bought and converted, ready for 
the computers and peripherals. 

Eventually , the Manpower Services 
Commission (MSC), succumbed to such a 
strong assault. Now it will be funding 30 
similar centres throughout the U.K. 

For those contemplating similar projects, 
the moral is clear: amass what you can from all 
the resources available, group togeiher with 
others of Like mind for strength* and start your 
computer or electronics centre. When and if it 
works, officialdom may well offer some tardy 
assistance; by then you can, to an extent, 
dictaie your terms. 

The notion that Webb had was a complex 
mixture; there exist s a mis-match of jobs and 
skills; job creation is best locally controlled; 
unemployed youngsters have plenty of nous 
and little schooling; education is most effective 
when motivated by a need to know; Integra- 
:ion of real practical work experience is a key 
feature of adult education. 

As an act of faith, on a first-come, first- 
served basis, and with self- motivation as the 



for the disabled 

main criterion for acceptance, 30 youngsters 
were taken on for a year as a Youth 
Opportunities Programme {YOP} project. 
Word of mouth seems to have been the main 
advertisement. Those who found out about 
and visited the Centre were presumably the 
more strongly motivated. 

With a teaching staff of six, [5 Pets, several 
Aim-65 boards, sundry other computers, test 
gear, etc.* their learning was in four main 
areas: the modern electronic office; elec- 
tronics, with an emphasis on the digital; 
programming* mainly Basic and Logo with 
some machine code; and prototype develop- 
ment which was directly practical, starting 
with no previous work experience. 

The success rate has been astounding. Some 
65 percent are now employed. No wonder the 
MSC was so keen to help; it cannot achieve 
this rate with university graduates, let alone 
poorly-educated youngsters. 

The regime, if such it can be called, is 
essentia Uv informal. Though lateness or non- 
attendance leads to a docking of the £23,50 
YOP wage, there is no stria timetable or 



curriculum. If someone should wish to play 
Space Invaders for two months to remove all 
trace of it from his system — ii rarely takes 
longer — then he will probably be left alone to 
do it. Sooner or liter, with this laissez-faire 
approach, a working understanding is reached. 
Only by giving the responsibility of action 
can responsibility be developed. 

The youngsters have two definite assets — 
they know when they do not know something 
and they have commonsense. Given a toolkit 
— soldering iron and pair of pliers — and a few 
components, they can star! making things. 
When they realise they do not know some- 
thing, then it is time for theory. For example, 
they might ask for ;i seminar on power 
amplifiers — to make an electric guitar 
sound better — or on analogue interfaces to 
input in a particular way to a computer. 

One of the weaker ureas is programming. 
The greater proportion of software uses 
mathematical modelling. How, then, do you 
teach someone with a totally non-mathematical 
background? Mew languages arc needed as are 
means of incorporating basic mathematics into 
the brief 12 months. 

The trainees are very good at problem 
solving and this shows, when they are 
designing, Having gathered components, 
discovered the necessary theory, in the end 
(hey usually find a very elegant final solution. 

Where arc the jobs at the end of this? Some 
youngsters have gone into apprenticeship to 
further their careers. Sound-recording studios, 
musical-equipment manufacturers and Space 
Invader emporia have taken on trainees. 
Further education, working for the Prestel 
service, and salesmanship arc courses taken by 
others. 

After a year's training they will have 
acquired some of their tutors 3 experience, ; nd 
the Centre clearly enhances credibility with 
local employers. By working with high tech- 

(continued on next page I 



K 




^5 ms ^M 


1 1l 



YOUR COMPUTER. DECEMBER 1961 17 



COMPUTER CLUB 



{continued fro/w previous page) 
nology, in an area of high potential* their self- 
respect and sdRonfidcncc is also improved. 

A few job$ have been created at ihc Centre. 
Integrated imo the scheme of things at the 
Dale art two businesses. As with any form of 
further education, real product are developed 
and manufactured alongside the educational 
process, 

Simon Browning runs a small firm develop- 
ing aids fox disabled people, With a $tart-up 
Capital of £40,000, they have a year in which 
to become established- If all goes well, simitar 
firms could be attached to ihe 30 centres 
throughout the country. Such a concept is, 
indeed, a powerful one. 

Not only does the design and development 
of elect ronics-baied aids provide teaching 
material and direct experience the manufac- 
ture and servicing will provide worthwhile 
jobs and much-needed equipment Tor the one 
in 10 of the U.K.** population who are 
disabled. 

Local support can be provided ai the 
Centre j backed by the teaching si a IF and 
engineering associates. Networking between 
centres means experience and design work will 
be shared, so cutting development costs. 

Need-based — as opposed to consumer- 
orientated — manufacture is not the easiest of | 
areas in which to start a business. There is 
little money available. The demand is there 
and there are many disabilities which can, be 
lessened through the appropriate use of high 
technology. 




[f you want to know what devicts they will 
be making, imagine yourself paralysed, or 
blind* or deaf Now think how you could use 
your computer to help. There is plenty of 
scope. 

If you spawn an original idea 3 forget it for a 
few weeks. Then if it still seems good, write it 
down and send it to the Centre* 

Richard Hillier is a well -qualified electronics 
engineer whv> has set up Counter measures Ltd 
alongside the Centre. Having developed high 
value-added .products — specialised data 
loggers, a polyphonic symhesiser, an EPROM 
blower, among others — the deal is a straight- 
forward one of a 50/50 split of profits in return 
for work space. It looks like a stable md 
worthwhile interdependence - 

Of course there have been problems, there 
have been breakdowns and not everyone has 
completed the course. As a whole, it's a 
definite success. The fact thae the Department 
of Industry's Education Department will be 
investing £6 million to £7 million in creating 



similar centres throughout the l\K. over the 
next year is a measure of that success, 

Chris Webb and three colleagues will be 
heading the Dol consulur.cy >ct up to handle 
this development, whkfa meant that it stands a 
beiter-than-average chance of success. They 
will provide technical and educational advice 
at an adult and community level as the new 
units are started in tandem 

The Information Technology Centres 
(ITECs)j as the Pre*-, has nominated ihern, 
will initially be situated in the depressed inner- 
city areas and will be modelled on the Netting 
Dale Cenire s taking into account current 
needs, local and indtmrkl resources, 

The beauty of a loosely-coupkd network is 
that it can be tailored to suit and adiusi to 
changes in local and immediate requirements. 
Prestel mB link the centres — information will 
be available on-line — giving an economy of 
scale, though autonomy can be a strong 
feature, integrating c^-h .;ni: into its 
individual environment. £ 



Computer Club is here to encourage you 
to start your own local computer club 
or, if one already exists to join it and 
become involved. Each month we will 
devote the page to new ideas from local 
dubs. We would like to hear of anything 
which has made a club a success, or of 
any projects or programs you are 
developing. 



RAM EXPANSION for 6502 andZ80 A Micros 




ATOM - PET - UK 101/ O.S. - TRS 80 
VIDEOGENIE and ZX81 



Prices; 



Expansion 
module 


Atom 


Old Pet 


New Pen 


UK /OS 


TRS80 


Videogenie 


ZXSf 


16K 


£40 


£40 


£40 


140 


£33 


£33 


£33 


32 K 


£52 


£52 


£52 


£52 


£45 


f45 


145 


64K 


£80 


rao 


CSO 


£80 


H3 


£73 


f73 


123K 


£130 


ET30 


£130 


C130 


£123 


£123 


£123 



PffCGS shown are for kit versions. Ptease add £S.QQ±VAT to aff prices for ready-tuft 
modi/fas. 

All prices include full components and documentation. Please add 15% VAT, 

'Extra power supply of 12V/ 1 A and — 5V/10mA required. You can either provide it yourself or we can 

supply it for you at £8 + VAT. 

Think of the future , , . and then get down to the basics. 

The power of your Microcomputer really lies in its software — and the power of its software depends 

directly upon the availability of Ram. 

Memory modules are now easy to install and low cost r So why wait? 

We have designed memory modules for the PET, ATOM, UK 101 /OHIO SUPERBOARD, TRS80, 

VIDEOGENIE and the ZX81. Off the shelf and ready to run. tn most cases p simply plug into the 40 pin 

socket of your Microprocessor and you get 128K, 64K, 32 K or 16K more RAM at your fingertips. 

How do we do it? 

We make the latest device in the field available to everyone — the Motorola MC 6665 

L20 or 64K bit on a single chip, which consumes a mere 10mA at 5V to retain your data or programs. We 

put eight of this on to a board the size of a cigarette packet to give you eight times the actuaf power of 

your Microcomputer 

If you do not yet know how to make full use of your 64/12SK H our latest documentation includes 

programming examples to start you off. 

Please write or ring us for further details: 

AUDIO COMPUTERS. 87 BOURNEMOUTH PARK ROAD, SOUTHENDON SEA, ESSEX 

TEL: 0702 613081 



18 YOUR COMPUTER, DECEMBER 1981 



TRS 80GENIE SOFTWARE 



from the professionals 



$ e o fl 

^ c ~ 






. .. 



w 






H" 



.^zr 



:::: 


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f ft ...a new, simple 
■■to use, moderately 
priced word processor 



The introduction ol a brand new word processor is a maior event and AJEDIT is without daub! 3 major 
program. There are, however, qyit© a lew Word Processors around ami most of them are extremely good 
ones - why, therefore, another? The quesiion is even more pertinent when it is known that we specifically 
commissioned the writing of it from an author of the status ol Denville Longhurst ol Enhanced Basic fame. The 
answer is that user feedback shows that a large number of customers do not need or want word processor 
programs which require a quantity of training before use Scrips.it, for instance, is an excellent program, but is 
complex to use; It even comes with a training course on tape, If one operator is dedicated to using the word 
processor then it makes sense to have her trained, and the more complex the program (so long as the complexity is 
accompanied by more and bigger functions) the better, 

AJEQIT has been written (or Ihe user who needs a word processor intermittently, say three or four times 
a week. Its prime design criteria was ease ol use - and just as importantly - ease of recollection of its commands. 
Take, for instance, the text editing commands - they are as close to the Basic Edit commands as possible, so that 
the user will remember them: To insert type 1 , to delete D. to take out three letters type 3D and so on. 

Furthermore, AJEDIT has benefited from being wriiien after a number of other word processors. The 
deficiencies in its predecessors are corrected in AJEDIT. For instance, any control characters can be outputted so 
I hat lull advantage can be taken of the features of the particular printer being used Disk directory access is 
available from withm AJEDIT as is the killing of files on the disk. The FREE command and a number of other DOS 
commands can be carried out from wlthfn ihe program with a return to AJEDIT - with its text intact. 

AJEDIT contains close to one hundred commands coven ng most word processor requirements. Dedicated 
printer commands for the Epson MX series and ihe Centronics 737 are Included - again for ease of use of these two 
popular printers. 

AJEDIT needs 48K and one disk minimum and is suitable for the TRS-BO Models I and lit and the Video 
Genie Models 1 and II 

AJEDIT ♦.*.„ „ E49,9S 

Inclusive of V. AT. and P. & P. 



MOLIMERX LTD 

A J HARDING (MOUMERX) 

1 BUCKHURST ROAD, TOWN HALL SQUARE, BEXH ILL-ON-SEA, EAST SUSSEX. 
TEL: (H24] 220391 / 223636 TELEX 89736 SOTEX G 

TRS-80 4 VJDEO GENIE SOFTWARE CATALOGUE tl .00 (refund a bl» J p!us 50p postage. 



s&W. 



YOUfl COMPUTER, DECEMBER 1981 19 



SURVEY 

VIDEO GAMES 



Sefwyn Ward's look at the 
major video-game computers 
reveals them to be far more 
sophisticated beasts than their 
pedestrian forefathers. Their 
improved display and definition 
heighten the effects of the 
latest adventurous games. 

RaCIMG TO the finish on a Grand Prix circuit, 
manoeuvring round trees and moguls in a 
downhill ski run, destroying hordes of mal* 
intent ioned Martians* and averting a nuclear 
holocaust , are some of the more soothing 
armchair experiences offered by the latest 
generation of plug- in TV games, 

TV games have advanced a long way since 
ihe beepheep of ping-pong tennis and soccer 
games filled Christmas stockings hot so many 
years ago. Now, games are altogether more 
sophisticated, considerably more expensive, 
and usually known by the more grandiose title 
of "video computer games". 

With Christmas rapidly approaching, we 
look at four video-computer game systems: 
Atari VCS, Philips G-700Q, Mairel 
I nielli vision, and the Inter ton VC-4QQ0. The 
Jnterton is similar to the Acetronic MPU 
1000, Radofin 1292/1 293, Frinzironic VC- 
6000, Teleng, Rowtron and Database 
computer-game systems. 

All the videchgame computers plug into the 
aerial socket of a conventional television — 
preferably colour, as they all generate colour 
graphics. All are equipped with game controls 
and a mains transformer. In the case of the 
Mattel Intel Li vision j the transformer is in- 
built. 

The video-game computers are described as 
^programmable" j although this does not 
generally mean that they can be programmed 
by the user. It refers to the fact that video 
compusers can accept plug-in cartridges which 
allows you to have a continually-expanding 
library of games. Inevitably, cartridges 
produced for use with one video-game 
computer system cannot be used on another. 

The Atari VCS has been on the scene for 
longer than its rivals and with a range of 
around 40 cartridges, it has by far the largest 
selection of games available. Cartridges vary in 
sophistication from relatively simple hat-and- 
ball games to complex animations such as 
Superman where aciion is limited not solely to 
the dimensions of the TV screen. 

The player — controlling an animated 
Superman figure — has to roam through a 
series of inter-connected displays, flying out of 
the left-hand side of one display into the right- 
hand side of the next, to capture and jail a 



band of desperadoes, find and rebuild the 
hidden sections of Metropolis Bridge? and 
change back to meek mild-mannered news 
reporter Clark Kent to file his story at the 
Daily Plawr. All of this while dodging 
Kryptonitt meteors which rob Superman of 
his powers — and for which the only cure is jo 
find and kiss Lois [ jne, 

Can ridges are also available containing 
excellent chess and checkers programs — I 
found that the Atari chess cartridge could 
usually better my dedicated+funetion Boris 
chess computer — as well as backgammon and 
Othello, which is also known as Reversi. A 
Bask Programming cartridge is also available, 
although it is extremely limited in scope. 

The Atari is best known for its versions of 
popular arcade games. Most video computer 
systems now include a Space Invaders can- 
ridge in their range, but the Atari cartridge 
mo$i closely reproduces the arcade game 
which has spoiled so manv pubs throughout 
the U.K. 

New Atari cartridges include Asteroids and 
Missile Command; again, both are based on 
arcade games and both have very fast action, 
indeed. New Cartridges fully compatible with 
the Atari are also now being produced by an 
independent company, Act i vis ion. These 
already include some three-dimensional sports 
games which compete directly with ihe 
generally more sophisticated sports-game 
cartridges available for the Mattel 
Intcllivision. 

Separate joysticks 

Unlike the other video-computer game 
systems which have multi-function game 
controls, the Atari uses separate joysticks and 
paddles, which means users have the task of 
plugging and unplugging controllers when 
changing between some of the cartridges. It 
also means that io use some cartridges, addi- 
tional controllers must be bought. In fact the 
controllers seem io be [he weakest feature of 
the Atari. 

The joysticks in particular are prone to 
jamming or breakdown. On the other hand, 
the Atari is the only video-game computer 
which — at least with certain cartridges — 
allows four players to compete simultaneously, 
provided you buy an additional pair of paddle 
controls. 

The Atari VCS* which can be found for 
slightly less than £100, is complete with a 
Combat cartridge which comprises a variety of 
tank and air-bait le games. Additional cart- 
ridges vary considerably in price from around 
£16 to £35, The newer cartridges tend to be in 
the £23 to £29 price range, although the 
Acti vision range costs around £16. 




I I 





20 YOUR COMPUTER, DECEMBER 1981 








Above: the tnterion VC-4QQQ i$ based on fA* 
$&me tfip as the Aceifonic MPU tfOft Redo/in 
1232/1293* Primtrotoc VC-60QQ, Tettmg 4 
ffowrron and Database systems. 

Top teft; the- tnteftwstQf) from Matt&t. 

F&t teft; there are 40 cartridges in the- Atari 
VCS games tibrsry, 

Beiow: Phifips* G-7000 video- ffome machine. 




The Philips &7QQ0 video game computer is 
an attract! vc!y-$iykd piece of equipment with 
a full alpha-numeric, touch-sensitive keyboard 
— although most of the Philips game 
cartridges use only the system's joystick 
controllers. 

The release of cartridges for the Philips 
G-7000 started slowly, although there are now 
about 25 in the range. As with the other video* 
computer systems, the range is varied and 
offers sports games, shooting games and maze- 
chase games. The number of game variations 
on each cartridge is mostly very limited, 
although some of the early Philips games 
cartridges included some curious combina- 
tions: one cartridge contained the odd mixture 
of anagram and car-rate games; another 
contained a lunar-landing game, a memory 
game and a Mastermind code-breaker game. 

Graphics on the Philips G-7000 are rela- 
tively crude. Often objects which are displayed 
appear as seemingly abstract shapes. There are 
occasional compensations, however — par- 
ticularly entertaining is the animation of the 
swaggering gunslingers in Gunfighter, who 
closely resemble a pair of saddle- sort* John 
Waynes, 

Some of che Philips cartridges are cleverly 
conceived and are peculiar to the Philips 
system. Stone Sling, for example, is a two* 
player game where each player control* a 
medieval soldier and stone caiapauh behind a 
towering fortress. 

Players fire their catapults at each other io 
eliminate their opponent's fortress or hit the 
opponent's caiapuli The fortresses crumble a 
little more each time they are hit until one i$ 
completely destroyed. Then the losing soldier 
waves a white flag to surrender. One of the 
newer cartridges, Basket Game, is also 
unusual in thai it is, in effect, a iwo-player 
version of the usually solitaire pinbali game. 

Limited scope 

The Philips G-7000 retails at about £95 and 
all cartridges are the same price at about £15. 
An assembler programming cartridge is avail- 
able which compares favourably with the Atari 
Basic Programming cartridge, but which is 
still limited in scope — not least because there 
is no means of storing any program which a 
user does manage to write. 

The most expensive of the video game 
computers and in many respects the most 
sophist icted, the Mattel Intelliviston system 
combines superbly-detailed graphics with 
relatively realistic sound effects. A range of 
around 20 cartridges is currently available, 

The Mattel controls differ considerably 
from those of rival systems. Each control has 
both a touch-sensitive keypad and direction 
disc. With every games cartridge you are 
provided with a pair of overlays which slide on 
top of the game-controller keypads and 
indicate the function of each pressure-sensitive 
area, The direction disc corresponds in 
function to a joystick. 

I found the overlays a very useful innova- 
tion, particularly given the number of 
functions used in some of the more complex 
games, I would, however, have strongly 
preferred a good* old-fashioned joystick to the 
touch-sensitive disc as a means of control, 

(continued on next page/ 



YOUR COMPUTED DECEMBER 1961 21 



t 





(continued on previous page) 

Many of the Maud cartridges feature a very 
acceptable simulation of three-dimensional 
graphics. The tanks manoeuvring in Armour 
Baltic are no mere inisslc-spoufing blobs* but 
detailed figures — although despite this, and 
the largt variety or terrain displays which can 
be randomly generated, the game has if any- 
thing less potential than the more conven- 
tional tank-battle games available with the 
other systems. 

More complex are the bank games which 
feature both strategic- and tactical- level 
combat. In Space Battle, fai example, play 
begins wiih a radar display showing five fleets 
of alien space ships moving in from different 
directions towards the player's mother ship. 
The player has three squadrons, each of ihrec 
fighter ships , to launch agamsi the approach- 
ing enemy. 

The radar display is used to deploy forces, 
but where a squadron inter ct pis an alien fleet, 
the player may switch to a tactical display 
where he can view the action as if from the 
cockpit of one of the fighter ships, The object 
at this stage is to shoot down the alien ships 
while avoiding their laser fire. Players can 
return at any time to the strategic radar display 
to check on progress of the squadrons and of 
invading fleets, 

However j where the Mattel system moves 
into its own is with its range of elaborate 
sports games. These involve fine detailed 
graphic displays showing complete animated 
teams ^ playing full-length games, and even 
featuring crowd noises. The team -sports 
games actually seem more complex than they 
really are, as player* each control only one 
figure at a time while the computer animates 
all the remaining figures, but they are 
certainly entertaining to play and watch. 

In Hockey, which is actually an ice hockey 
game, the can ridge even provides for fouls and 
player figures being sent off to the penalty 
box. In Skiing, among the most enjoyable of 
the Mattel cartridges, players take turns to 
race against the clock anoVor each other on a 
variety of downhill or slatom runs, dodging 
trees and jumping moguls, manoeuvring the 
skier figure by altering the angle of his descent 
down the mountain. A Soccer sports-game 
cartridge is supplied with the Mattel 
Intellivision video-game computer, 

Thf Mattel retails at around £2QQ f which is 
perilously close to the price of some genuinely 
programmable^ and more versatile, home 
computers. 

There is> however, no programming 
cartridge available for the Martel> although 



Left: the Database ganws computes 
and Above, two of rh& fatasr 
cartridges for the Alan VCS. 



plans have long been announced for the intro- 
duction of an add-on keyboard to convert the 
Mattel Intellivision into a home computer, 
There is still no news of when the keyboard 
will be available in the U.K. nor of how much 
it will cost. Mean while , Mattel cartridges sell 
for around £19. 

Typical of a number of video computer 
games, each with similar range of cartridges, 
there are currently around 25 cartridges 
available for the Intcrton VC-4000- 

The Intcrton uses multi-purpose controllers, 
comprising a joystick attached to a keypad 
over which overlays can be fitted. I found 
these controllers easier and more convenient 
in use than those of the other video computer 
-systems. 

The cartridges themselves are varied but 
generally unremarkable. Some of the combina- 
tions are very good value — Car Racing 
includes gams where the object is to avoid 
crashing into on-coming vehicles, games 
involving a race around a circuit, and night- 
driver games where [he object is to stay on a 
sharply winding road. In the Atari system, 
where versions of the same games can be 
found, these are spread over three separate 
cartridges. 

Nevertheless j the graphics and sound -l- fleets 
generated by the Intenon system are 
extremely crude by comparison with the Atari, 
Mattel and even Philips systems. For some 
inexplicable reason, tanks or planes blown up 
in Tank/Air Battle do not explode, they 
enlarge to several times their original size. 

Also in this cartridge r the planes in air battle 
games have the irritating habit of freezing in 
mid-air when they reach the edge of the screen 
rather than Hying around the oiher side ol the 
screen as is the case with similar cartridges for 
rival systems. 

The Intcrton VC-4000 retails for around 
£95, including a Space Invaders cartridge. 
Additional cartridges arc around £15. Some of 
the similar video-game computers can be 
found from around £65, although usually the 
cartridge supplied is only a bat-and-ball game 
cartridge. 

Vjdeo*compiKcr games are likely to prove 
more than just a five-minute wonder in mwi 
households. With the new cartridges for all of 
the systems being released all the time, it is 
Likely that your bank balance will run out long 
before your family's enthusiasm. 

It is a sure bet 1 hat Santa will be delivering 
many video-computer games this Christmas — 
but do not be surprised if he's still elbowing 
his way through the kids to the front of the TV 
well into the new year. 



HOME COMPUTER RETAILERS 

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22 VOUR COMPUTER, DECEMBER 1981 



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TheTI-99/4A 

The Home Computer 

worthy of the name. 

J The TI-99/4A comes with TI BASIC built 



Even if you're new to computers, you'll 
be using the TI-99/4 A with i n m mutes t )t pit iggi i ig it 
into any standard TV set, Because the Tl-99 /4A is a 
true computer lor the home. Immediately accessible 
to the whole family. All t< >r around £.299^ 

Just snap in one of our wide selection of 
Solid State Software? Command Modules, touch a 
few keys, and you re ready to go. The 40 modules 
can sharpen your children's maths, teach you to win 
at chess or even help you with household financial 
decisions. And much more besides. In all, over 400 
programs arc available. 

All enhanced by full music capability and 
16-colour graphics. 

Another development which sets the 
11-99/4 A apart from the rest, is our optk mal St >(id 
State Speech* Synthesiser. Actually reproducing the 
human voice. With our new Emulator Command 
Module! its vocabulary is unlimited 

For data input output you can use an 
ordinary audio cassette recorder. And a lull-size 
professional keyboard makes it easy to use. 



in. 

[deal tor when you want to learn programming - 
and to get you started there's our "'Beginner's Basic" 
course, free with each machine yet powerful 
enough for even the most experienced programmer. 

To help you get the most from the Tl 99 4A 
you can join the independent users' club. And there s 
a special magazine (" Wer") available through 
dealers, or on subscription. 

So, if you're looking for a home computer, 
you eaiVt afford to miss the "IT99/4A for versatility, 
power and value for money. 



* I6K KAM. fcxpimdnblito iSK 

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REVIEW 

ZX PRINTER 



The new £50 printer from 
Sinclair means hard copy at a 
soft price. Eric Deeson 
assesses the device. 

Perhaps £50 seems a considerable sum to pay 
for an add-on to a £.50 computer* but the ZX 
printer is a miracle at this price. Superbly 
designed, the cigarette-box-sized machine is 
inexpensive to run and gives impressive 
results. If you bear in mind that it speedily 
reproduces all the Sinclair graphics, you soon 
realise that it would be remarkable at several 
times the price, 

Mechanically; the system is a neat applica- 
tion of a standard approach, A spark-emitting 
stylus scans the aluminium-coated paper, 
burning away the metal to create the black 
points which form the "printed" character. 
The line of sparks is a pleasure to watch. 
There is a very slight smell of burning, and 
the residue of burnt paper soon lines the stylus 
tracks, 

Prim quality is good* although there is 
sometimes a slight distortion in the verticals. 
Occasionally s the black smears on to the white 



Technical Specification 
Power Pack 

SiiE#: 10 by 7 by 6.5cm, 
Weight: 6259m. 
Output: 9V, 12ft, Unregulated, 
Cost: Included In price of printer. 

Prirttir 

Si*e: 14 by 9 by 5,5cm. 

Weight; 400gm. 

Power: From the computer. 

Paper: Electrostatic . 

Rolls - 19.3 by 10cm. 

Five rolls El T. 95 — one supplied. 
Resolution: 256 by 256. 
User graphics Yes. 

Expandability- Via connector to computer. 
Cost: £49.95 including VAT, postage and 
packing. 



and makes inverse characters rather hard to 
read. Even normal characters can be confused 
more readily than on screen — "I" may be 
mistaken for I and the numerals 3* G> 5 and 6 
are sometimes indistinct This makes reading 
ZX printed listings rather tiring — especially 
with graphics and machinenzode routines. 
Generally j print quality is perfectly adequate 
— photocopies made from the listings are 
good. 

The ZX printer is supplied in the standard- 
size Sinclair foam box* with a heavy new 
power supply, and a 16-page booklet with 
guarantee. The power supply replaces the one 
which fed the ZX-81 and is welcome because 



of its long leads. It becomes only slightly 
warm — the temperature of the computer gave 
me more concern. 

The ZX-8I white-out problem is no more 
frequent than usual — even with the 16K 
RAM in position. However* one must now be 
even more careful during long programming 
sessions with the 16K. The printer plug fits 
into (he RAM-pack position* and the RAM 
pack fits into the plug. The result is 
surprisingly si able, but must be less reliable 
than using the 16K connection alone. 

The ZX printer is not silent — the corollary 
of its design. All the same, the noise is not 
excessive, and if there is vibration — as there 
must hu — it does not disturb the nearby 
RAM, 

The paper- roll holder is easy to attach and 
detach, to unload and toad. When reinsert ingj 
however! push it home with an extra jog for 
luck to ensure that the clips are correctly 
located, The serrated t eater will presumably 
become blunt relatively quickly but works well 
as long as you hold the roll while tearing off 
the copy. 

The printer's only hardware control is the 
paper-feed button. Very occasionally, this 
becomes stuck. In fact* I already bypass it in 
most cases by using Copy, Break, Otherwise* I 
use software control, as detailed in chapter 20 
of the manual. While the printer is working, 
video synchronisation is lost — so, if you write 
a program mixing outputs to printer and dis- 
play, do not put the instructions too close 
together; Pause 20 is enough. 

The cursor homes, too, so you are obliged to 
reposition it using cursor control The Copy 
command reproduces the contents of the 
screen-display area on the printer, including 
empty lines. It does not reproduce the message 
lines, so comma nds, report codes and input 
prompts do not appear. On the whole, thai is 
acceptable, though I have already had occasion 
to wish it were otherwise, Break and Com 
work with the printer as with the screen 
display, though Cont does not always give a 
perfect join, If-Then Copy is a useful 
technique. 

Of course, you cannot use the printer for 
animated graphics games. However, repeated 
graphics patterns are really beautiful — the 
mix of striped black and silver is very striking. 
A few home users are bound to be tempted 
into creating designs for greetings cards. 

The only standard printer feature missing is 
Echo — reproduce on the printer what is 
entered at the keyboard. This has a number of 
uses, not least allowing one 10 program away 
from the den without a bulky TV set, The 
obvious starting command is LPrim InkeyS, 
but that is not more use than Print InkcvS. 




Technical 



Stephen Adams approaches 
the ZX printer from the 
technical angle. 

The instructions for most printers are at 
best sketchy, but those supplied with the ZX 
printer are most detailed and simple, The 
instructions for using the printer in a program 
are detailed on page 1 33 of the ZX-81 manual 
and are not included in the printer's 
documentation. 

There is also a clear explanation, illustrated 
with drawings, on how to load the printer with 
paper which is the only complicated aspect of 
using the machine. Although Sinclair reconv 
mends its own aluminium-based, electrostatic 
paper, others can be used. 

The feed button is the only control on the 
printer and when pushed, advances the paper 
a line at a time, Nothing can be printed while 
this button is depressed. When the printer has 
finished a 65ft. roll of paper, it needs 10 be 
cleaned. You can use a child's paintbrush to 
clear the burnt aluminium top paper from the 
recess under the paper carrier. 

The printer is activated by addressing a port 
with address line A2 tow- This is the usual 
form for Sinclair and, of course, reduces the 
number of input/output addresses available to 
the user. The official address for the printer is 
port FB which i& both written to and read 
from. The printer also appears at other 
addresses so if you write machine code to 
access any one of these* you need to change it 
before you use the printer. A summary of the 
data bits and their uses are given in table L, 

The programs provided in the manual vary 
from a text justifier to a high-resolution plotter 
which enables the user to define every dot on 



24 YOUR COMPUTER, DECEMBER 1981 




aspects 



Tablet 

Data Sit Use 


Raed Write 


DO 


DOT STROBE 


X 


D1 


MOTOR SLOW 


X 


02 


MOTOR STOP 


X 


D6 


PRINTER EXISTS 


X 


D7 


HIGH VOLTAGE TO 
STYLUS 


X 


D7 


STYLUS ON PAPER 


X 


Not*: Conditions active on binary 1, 
opposite on binary 0, All conditions are 
latched. On pressing feed button, D1/Q7 
are low and D2 high , 



[he primer. As this resolution is 256 by 256, 
[here are 6S S 536 dots to define and as can he 
expected, ihat occupies 8K for the array alone. 
It means, however, that very accurate graphs 
and user- programmable graphics can output to 
the printer. Naturally t calculation* concerned 
with these graphics slow down printing speed 
— in the Fast mode* the high* resolution plot 
program takes four minutes to complete, 

All printing is done in Fast mode which 
means [hat there is no screen to watch while 
the printer is printing. A full screen can be 
printed by the command Copy and cukes 13 
seconds. 

LPrint prints 2 line pf text to the printer 
instead of [o the screen and uses, the same 
format as the Print command. The only 
command which cannot be used is At, but you 
can use Tab in its place as the LPrint prints 
only one line at a time. LList lists the program 
lines and can be set to any line in the program, 
LList will* howeveij only stop at the end of a 
program. 

The printer is plugged into the hack of the 



ZX-80 or ZX~Sl; its connector neither binds 
on the case or wobbles when a key is pressed, 
The connecting lead is only 3in. long, very 
stiff and must be placed on the right-hand side 
of the computer. 

The 1 6K RAM pack plugs into the back of 
the Connector if you have one. No problem 
was found in using the RAM pack since 
Sinclair Research has provided another power 
pack rated at 1 2A to replace the existing one. 

The new power pack must be used — the old 
one rated at 700mA cannot cope. The new 
power pack has several design changes as it 
uses two power silicon diodes instead of the 
previous potted-bridge rectifier. It has also 
increased the size of the smoothing capacitors 
from 2,000^f to 32*000^ It no longer plugs 
into the wall socket, but has a mains lc*d of 
5ft. and no plug. This means you can position 
your equipment further from the power point. 
but you now have 10 go and buy a plug before 
using it. I: would be better lfStnclair provided 
a plug so that the machine could be complete 
and ready to go as soon as you receive it. 

Once the printer is connected, the power can 
be turned on. You will hear a short whirr from 
the printer as it lines up its starting point. 

The printer is relatively quiet during normal 
operation, but when printing makes a noise 
like a clockwork toy, whirring and spluttering 
until printing is, (nibbed The blue flashes 
under the transparent Pcrspex shield show the 
printer at work. Its stylus runs Fixed to a con- 
tinuous belt and burns away [he aluminium. 

When it has finished printing, the paper 
must be advanced — there is no spacing 
between pages — if you wish to tear the paper 
on the serrated edge provided. The print is 
very clear and the inverse graphics excellent. 
It can be very easily photocopied for a 
permanent record if you dislike the shiny 
surface, 

A test was done on the paper to sec if the 
print could be affected by heat as some electro- 
static papers are. After three hours sitting 
above a gas fire* no deterioration could be 
noticed, The paper does, however* pick up 
grease from the fingers although it does not 
affect the clarity of the priming. Creases in the 
piper can crack the aluminium surface, but I 
noticed, no flaking of the surface. 

The paper was also soaked in water and 
dried by a fire to test its extremes; the paper 
did not lose its white bucking or the quality of 
the print. Altogether it seems satisfactorily 
indestructible. There are no gaps between the 
graphics so a continuous line can be created. 
Nor are there gaps between lines so you can 
print whole pictures — size of the characters is 
2.5mm, square. 

The paper is 10mm. or 4 in. wide and only 
one 65 ft, roP is provided with the printer. 
Replacement rolls are available from Sinclair 
Research at £1 1.95 for a five-roll pack. 

Removing the [op or the printer to look at its 
ins ides is not a practice I would recommend as 
traps lurk for the unwary which might wreck 
the machine. 

The logic is contained in a single uncom- 
mitted logic array chip or VIA which has 
been specially programmed for Sinclair to 
control all the functions of the printer. It does 
several jobs: 

■ Puts out e strobe signal on Do. 

■ Controls motor on and oft, plus the slowing 



of the motor near the end of the pf toted line, 

■ Checks that the stylus is resting on the metal 
Strip on the left-hand Sid* Of the printer 
hefore printing. 

■ Decodes all addresses to the printer and 
latches them. 

Apart from the ULA, there are various 
capacitors, resistors and a high- voltage 
transformer all mounted on a single-sided 
prinied-cireuit board, The motor and cable 
also terminate on this board. Under the board 
is a strobing disc which contains slois lo tel) 
the light-depcndenl resistor whether it is 




covering a black line or not. This makes sure 
that all 256 dots are printed in the same place 
each time and do not depend on the motor 
speed. 

The motor drives a plastic worm gear to 
drive the paper up. A belt-driven system takes 
the stylus to where it should print each dot. 
This belt is carried between two pulley wheels 
whose ends are located in the top and bottom 
of the case. The belt is made of ridges which 
slot into grooves in the pulley wheels so there 
is no slipping. 

On top of the belt the printing stylus is 
mounted — two pieces of wire are wound 
round a spigot on top of the belt. The wire is 
bent so that one end sticks outwards to write 
on the electrostatic paper and the other points 
inwards to connect with a metal truck running 
inside the top of the case along the paper. 

The stylus had to be made from special wire 
since it uses a high voltage to burn away the 
aluminium coating and must be able to 
tolerate the wearing away of the tip by these 
voltages 

The power for this machine is taken From 
the 9V line and this means that the voltage to 
the input of the regulator is lowered. It also 
means that the regulator runs cooler even 
though the printer does take some current 
from the + 5 V regulator. 



Conclusions 

■ The printer is welt made and robust 
and the paper-feed button is the only 
control on the printer. 

■ The printing quality *s excellent and 
the paper is virtually indestructible. 

■ The paper can also be replaced by 
others although this is not recom- 
mended by Sinclair 

■ Loading paper is simple and well 
illustrated, 

■ It is, on the whole a very efficient and 
above a El inexpensive machine which 
should delight the user. 

B The programmer is catered for under 
the technical section if he wishes to 
write his own printing routines. 



YOUR COMPUTER, DECEMBER 1981 25 




£4.25 



*80 pag&s Explaining clearly how to *0u*vi* a compucirty quart out of a 
Sinclair pint pal. 

■ Saving Space - vital reading lor alt ZX8I ownen. 

* U no* f 5 tending the Display Frle lisircj The display ''le as memdry, 
clearing a fV3 f t gl Ehfl display. g^n9 E0!c*nS n PRINT sEatflmfinEs. 

■ Convfiftpng £XB0 programi - okpiaimng simpfy but comprehensively 
hflw to convert ihe hundred? of published ZX80 duo -ami. 

* Chaining Program* — r&vfc3Jinfl WchniquftS for passing data baTw&an 
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* Machine Code Pfoojarrts — all you vvani Tp knpw about Z&Q m&ehina 
language. Explaining how Ec- write, load, edit and save mac nine code 
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final chapter const&ti ol twtfua uselul, intaresling and enTeftein-ng 
programs such a* LINE RENUMBER, BOUNCER, SHOOT, STATISTICS 
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ZX81 • Video Genie* TRS80/LII 

Asset Stripper Compete against your ccunputer controlled 
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lucrative assets. Can your micro really outwit you? 

Kingdom of Nlm As ruler of Nam you must control its 
economy; allocating labour; building cities, factories and ships, 
importing and exporting; negotiating pay claims and fighting the 
looming threats of inflation, strikes, starvation, overpopulation 
and revolution. How long can you stay in power? 

High Stakes Buy, sell, train and bet on racehorses. An 
opportunity to make money shrewdly and spend Ix recklessly. 
Scrolling racing commentary. One or two players. 

Invaders Your planet is threatened by outer space invaders who 
will use their ultimate weapon if you lit them get too close! (not 
yet available for ZXB11 

Word gram We have yet to see a better version of this popular 
word game. Guess jumbled words of frll In the blanks, using the 
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Party Bran Tub Lots of programs - including one of the best 
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INTERVIEW 

RICHARD FOTHERG 



Richard Fofhergill 
heads the 
Microelectronics 
Education Programme 
which Is backed by 
£9.5 million of 
State funds. Bill 
Bennett visited him at 
his North- East base. 



Thh programme is run Irani a sm j LI 
semi-detached house on ihc campus 
of Newcastle Polytechnic^ a short 
ride on the new Tyne and Wear 
Metro from the centre of the city. 
After we had met and I had been 
introduced to the staff, there was One 
burning question: "Why run such a 
seemingly important prorrct from 
such a remote location 11 ^ The 
answer provided not only justif- 
kaiian, hut also a deep insight into 
the mind of the man who leads a 
team with a very important job, 

"I was already working in 
Newcastle a a a teacher trainer on 
this polytechnic litej I didn't really 
want to move anyway as 1 like it 
here. However, if microelectronics 
can do alt that we are told it can, 
then it should present no problems . 
The one advantage of living in rhe 
microelectronic age is that one 
doesn't have to travel to work; the 
work can travel to you. Information 
transfer is readily- available and we 
ace using it". 

What about (he inevitable i ravel- 
ling that needs to be done in ihc 
coiuse of your work' "Newcastle is 
fortunate in that is has excellent rail 
Jinks: the Inter-City IJ5 trains mean 
that London is just over three hours 
away. Most of the travelling is done 
by the information team, though. 

"One advantage of our location is 
the peace and quiet — there is no 
busy traffic passing our windows alt 
day. It means we are left to get on 
with our work here. The only dis' 
turbance is the occasional cheer from 
the football pitch", Cheviot House > 
the nerve-centre of the programme is 
located MSI to a sport field. 

Having disposed of the question* 
regarding what now seems like a 
wise choke of location, 1 asked 
Fothergtll to sketch ihe background 
to the DES Microcomputers in 
Schools programme. He at once 
pointed out that it was a micro- 
electronics in schools and not just i 
microcomputers in school) pro- 
gramme* and that The scheme was to 
cover pupils from the age of five 
through to 3 .3 



The Sum of £9>5niiLlion index- 
linked to the 1979 value had been sei 
aside for rhe programme by Neil 
M&cfarlane, the then Parliamentary 
Under-Secretary at the DES k and the 
programme was to be run from 
March 19-80 for five years, In 
November 1980 Richard FothergiU 
was appointed director. 

"When I had assembled a learn, 
we proposed a strategy, in effect, we 
began implementing our plan from 
February 1981, but il didn*l begin 
officially until April, It was decided 
to concentrate on three main Bitty 
which? for the want of better titles, 
we have called: resource, teacher 
training and curriculum develop- 
ment which is realty a catch-all We 
decided that because education is 
run in this country by local author- 



'We ate on 

the verge 

of an explosion' 



itit$, we realised the importance of 
involving them. 

"The money we were given was 
not enough to make us significant to 
each individual local authority T so 
wc divided the country Law 14 
regions; 12 in England, and one each 
in Northern Ireland and Waks, The 
Scottish run their own show from 
Glasgow, Both groups work in co- 
operation with each other, 

"The resource pan of the pro- 
gramme is designed to provide 
teachers with the support and 
information they need. It is vhal that 
we can keep these teachers up to date 
with all the advances that are 
constantly taking place, 

"This will be done by using 
regional information centres,, exhibi- 
tions, as well as the more traditional 
access to books. There will be some 
machines and some software set 
aside for the purpose of demonstra- 
tions which should enable teachers 
eo see the applications 1 ' 

At the resource centre at New- 
castle Polytechnic, in the middle of 
the door, is an exhibition , mainly of 
posters. Around ihe edge of the 
room were all manner of teaching 
aids involving microelectronics* 
ranging from the Texas Instrumenis 
Speak and Spell game to Pet, Apple 
and Research Machines micro- 
computers, and even a word pro- 
cessor. To the side of the main room 
is a smaller one — this is where 
teachers are taught how to use the 



latest in new technology' devices. 

Teacher {raining is the second or 
the three points in the programme. 
"We train teachers to think of the 
computer as an instrument, we 
show them how it can revolutionise 
the oflke — indeed, part of the 
teacher -training programme is 
devoted to familiarising teachers 
with the electronic oiTkc. 

"We also train the teacher to use 
the computer Tor computer-based 
learning. I call it that because of the 
confusion between the existing 
cerms such as GAL* CAI ete^ which 
all mean separate things, Computer- 
based learning is my phrase to cover 
this. 

'There is in fact another area in 
which we train teachers; that i5 in 
technology. There is in existence a 
course in control technology and 
electronics — run by ihe Joini 
Matriculation Board. This takes in 
[ust about everything from the 
switching of one t ran s istor right up 
to control devices and beyond into 
the world of microcomputers and the 
add-ons. 

"The third part orour programme 
is called curriculum development, tn 
effect, it covers everything not 
covered by ihe first two pans. 
Through this part of the programme 
we provide schools with relevant 
hooks, films and charis. 

"Although in the main the work is 
done via the regions, we held back 
some funds to use centralEy, This 



roottty will be spent on what we call 
our national activities, The in* 
,ct training of teachers by the 
Open University is an example of 
thiv 

"One of the tasks facing us is the 
establishment of some standards, we 
will gssue guide-lines on how to 
Configure equipment, lor example. 
This needs to be done because safety 
is an important factor in the class- 
room w/c shall also advise on 
operating systems as well as 
languages and delects. This will be 
done by a process of evolution — we 
will not lay down hard and fast 
standards, mainly because we 
couldn't make ihem stick. This, 
means we ■■- ave to evolve a set 
of agreed ^andiiLk 




28 YOUA COMPUTER DECEMBER 1981 



ON EDUCATE 



"Special education is an area 
which some of the centrally provided 
money is being spent. This will be 
m«d on making provision for handi- 
capped and retarded children. There 
will be special software for those 
children wish learning difficulties — 
for example, simple maths exercises, 

"Special add-on devices can be 
used K> help children express them- 
selves. One such device is a, box with 
coins struck on pads, ihe children 
can relate to this form of input 
easily, There is even a rubber for 
them lo press if they wish to erase 
something. 

"To the physically-handicapped 
child, the computer is more 
important as a communication aid. 
This is really a matter for the 
Department of Health and Social 
Security; we are more interested in 
education. However* one ust-ljl 
device ts an upside *down Tuppcr- 
ware bowl. It has shapes on it: 
pressing these shapes in various 
orders causes different noises to be 
emitted, This is a particularly 
valuable aid for teaching autistic 
children spatial skills". 

I asked Richard FothergUI if there 
was a tie-up between his programme 
and rhe Department of Industry 
{Dol J scheme whereby half the fundi 
are provided to any school which 
docs not yet have a micro, so ihai it 
may buy one: "I call this the Dol 
half-micro scheme; 1 hope thai it will 
soon be extended. So far about 1,600 
to 1,750 schools have taken part in 
This scheme, 

"We are supporting the scheme by 
offering io train teachers from the 







y 



t 



schools involved. This means that 
two teachers from each school will 
cake a four-day in service training 
course to learn about their respective 
computer, We are also supplying 
[raining materials. However, the 
scheme does have its timi tat ions - 

"Of course, it is only correct that 
any Government -funded scheme 
should support British micro- 
computer manufacturers. But to 
simplify the administration of the 
scheme, there are only two packages 
available — a yes or no choice 
between two systems which 
represent I he iwo ends of the price 
range r The choice of machines is 
restricted to the Research Machines 
38Q-Z, which is commonly available 
and hence the best machine, or the 
new EEC micro, which looks as 
though it will give plenty of 
development possibilities. 

"Under the circumstances, this is 
as good a selection as could be made. 
The Acorn Atom has a proven track 
record; the BBC machine will be in a 
form that is bound to be successful. 
The 330- Z is a machine which Is 
well proven in schools and is a solid 
machine — it can lake the treatment 
the schools will give it. The 
machines are the DoI b s choice 
though, not ours". 

So what kind of feedback his 
Pother gill received from the local 



'Safety is 

important in 

the classroom' 



education authorities (LEAs}? 
"Positive" j was the immediate reply. 
"Many comment on the time scale of 
'.he project. For some it can never be 
fast enough; others have adjustment 
time problems. The LEAs have been 
supportive — ihcy especially wel- 
comed the teaching packs On the 
whole everybody in the public sector 
js pressed For funds, so we are 
pleased that so many schools are 
prepared to spend money on micro- 
computers". 

Many Yvur Compute readers will 
be interested to hear Richard 
Fothergilfs ideas on selecting a 
home computer, especially with a 
view to education. First, I asked if he 
had any views on the trend towards 
home computing: "The future of the 
U.K. depends on the imagination of 
these people, A Sinclair connected to 
the television is more entertaining 
than the TV programmes on it M . He 
points out that one of the aims of the 




The MFP team front feft to fight: Mike Bostock t technology manager, 
Ri'ch&fd FQlftergi& e director, N&JQn Hinders, programme asstsfant. J&hn 

Anderson, deputy director. Bob Coates, computing manager. 



project is to stimulate and excite the 
next generation about micro- 
electronics. He also says he would 
At.c to see an interface for the ZX 
microcomputers. 

If a parent was considering 
purchasing a home computer for a 
child to learn programming, what 
should he or she look for: "First, a 
machine which can be attached to a 
TV, sfabie lettering, a good 
character display. A simple approach 
to Basic is important as is a good 
manual — in fact there isn't much 
point without one. Good graphics 
would be a bonus. Simple dumping 
probably to cassette* but with the 
ability to expand to discs later, 
expansion to colour* comrnumca- 
ttqn h and viewdata should all be 
considered as well as the easy 
memory expansion. 

"If ihe children were under 12 
then any good Basic machine would 
do. I think the RS 232 interface is 
preferable to the less popular 
Centronics type. With the possible 
exception of the Sinclair compute r fc a 
bare minimum of storage would be 
SK. This would soon need updating 
to I6K. and as soon as the children 
want to use databases, as much 
memorv as possible should be 
added 1 '.' 

Much has been said over the past 
year or so about the desirability of 
structured languages; what about 



this trend? ''There is definitely a 
trend towards structured languages, 
but the initial hump of micro- 
computer work has been done, All 
future development must take 
account of thi*. Movement will be in 
this direct ion p as in the Basic chosen 
for the BBCf micro, which is three- 
quarters Comal, Things Like this 
cannot be done fast. 

"The Microcomputers in Schools 
programme did not adopt a language 
as such — we were stuck with Basic, 
but let it evolve' \ 

What about the less gifted children 
— is u possible that the introduction 
of microcomputers in schools wilt 
see i hem further and further behind? 
"Not at all, the early computer* 
aided-lcarning programs were in the 
main designed lo help the less-than- 
avcragc child, tf anything^ the 
microcomputer will help these 
children by giving ihcm the plod- 
ding, patient tutoring that they need. 
In fact, it is a deliberate policy of the 
programme to ensure that the below- 
average child gets a chance. 

'" Education today is at a cross- 
roads, what we have now is a period 
of transition. Tor the first time the 
majority of schools have micros. In a 
year or two schools will have several 
more machines which will be 
scattered around in different 
departments — we are on the vergt 
®i an explosion". | 



YOUR COMPUTER, DECEMBER 19©1 29 




CHESS 

END-GAME 



Exotica such as the king ripple 
and the pawn-advance routine 
are two of the techniques John 
White has incorporated into his 
entertaining chess program in 
Basic, End-Game. 

END-GAME has been written in Basic to 
complement the draught program J-Checkers, 
published in the October issue of Your 
C&mputfr* It exemplifies the method of move 
assessment known as iterative deepening. 

I have chosen the endgame of chess as a 
model because it limits the number of pieces 
used and because the concept of mobility — 
essential in full games of chess — can, at i 
pinch, be ignored to keep the lime uken for 
the game within manageable limits, 1 have 
eschewed fancy time- or memory saving tricks 
for clarity, 

Having tested this program, I have satisfied 
myself that if is not possible to write a 
satisfactory program for playing a chess end- 
game using a look-ahead of only two-ply. I 
hope this information will be of use to those 
contemplating writing their own chess 
programs, 

End-Game does, however, play a frac- 
tionally more sensible chess end-game than 
many of the weaker chess computers available 
commercially, bearing in mind the fact that a 
compiled version would run in about two 
seconds. The interpreted Basic version 
presented here reqwres an average of two 
minutes a move, 



The end-game of chess is hard for a human 
to play well, but very difficult indeed for a 
chess computer, A human can easily see at a 
glance what wUJ happen six iq seven moves 
ahead for both sides — grandmasters can see 
much j much more. 

A chess computer will normally only analyse 
two or three moves ahead — four- to six- ply — 
although one or two of the most modern 
machines switch in extra routines for the end* 
g:ime when ^jfkjeiirly inttc material remains 
on the board- Under these circumstances up to 
five moves ahead — lOply — may be 
evaluated r Even so, the play is still weak by 
human standards, The classic problem is that 
shown in figure L 

It is possible for a human to sec at once thai 
black's only sensible move is K-B6 — or B8 or 
B7. Anything else loses the pawn to while's 
attacking king. I shall avoid the problem of 
whether bbek can win even if he does save the 
pawn. Yet very few chess computers can see 
this solution, and most play pawn endings 
very badly, moving pieces almost at random. 

Since the necessary deep search to play a 
good end-game is very ume<onsuming, 1 have 
tried in End-Game to produce an evaluation 
function which will play a recognisable end- 
game superior to that of most chess computers 
but using only a two-ply search. Essentially 1 
have relied on the well-known maxim of 
"Push a passed pawn 1 *. 

End-Game is written in Basic which 
imposes its own stunning restriction on what 
can be placed in the program: interpreted 
Basic runs some 200 times more slowly than 



the machine code used in chess computers and 
a complete game of chess is out of the 
question. Restricting the pieces to pawns and 
king only gives a respectable game with a clear 
objective: advancement of a pawn to the eighth 
rank. 

The first player to do this has essentially 
won at chess, and has won End-Game out- 
right. It may be noted thai the powerful 
Sargon 2,5 and Morphy chess programs also 
adopt this policy in their end-game play, and 
will make any sacrifice to delay the arrival of 
an enemy pawn on the eighth rank. 

End-Game uses a single subroutine to 
evaluate the position arising after each move — 
instead of evaluating the merit of each move 
itself* a strategy employed in other published 
games. The moves of each piece arc generated 
by the program which assigns a score lo the 
position arising from each move at the first 
level of search — one-ply, 

The moves are then sorted, using a fast-son 
routine which arranges the score in order of 
decreasing merit. The moves creating the 
scores are also rearranged* of course. 

The program now calls itself — an example 
of recursion in Basic — to generate the 




Figure t. The classic chess pf&bfem. 



responses to its sorted moves. It assumes that 
the opponent will be trying to maximise his 
score, and thus minimise the machine's score. 
So the best — lowest -scoring — opponent 
move is stored in location. 

This is combined with the first-ply score 
and compared with the highest total yet found 
for a program move, which is stored in 
location R(0). R(0) is continually updated as 
better moves are found for the machine — 
moves for which the opponent can find only 
weak responses. 

An importune feature of this search is the co- 
called "alpha beta pruning". If any opponent 
response makes the machine's move under 
consideration worse than a previous stored 
machine's move, then there is no need for the 
machine to consider any further responses by 
the opponent to the machine move under 
consideration. The flag "AB" is set to 1 9 
which stops any further searching of thas 
move. 

Alpha-beta pruning can save a good deal of 
unnecessary searching and thus a great deal of 
time. It is widely used in chess computers 
today. To be most effective, it is best to 
consider the most-likely-best machine move 
first* and also the most-likely-best opponent 
response. 



30 YOUH COMPUTER, DEC€MBE* 1901 



The most- likely-best machine move has 
been derived by the sort which we considered 
earlier. The mos [-likely-best opponent move is 
hard to determine without going through 
I hem all — which, of course, defeats the whole 
point of alpha- beta searching. 

I have instead adopted what I believe to be a 
novel heuristic: the best response found for 
the opponent for the previous machine move 
is evaluated first for the next machine move. 
This ha* proved 10 be quite effective m saving 
time in End-Game. 

The ncu effect of alpha-beta pruning on 
End-Game is quite spectacular in reducing 
respqnsc nnn;. Anyone who doubts this should 
try deleting tine 800. 

The whole process I have described — move 
generation, sorting, counter-move generation* 
alpha-beta pruning — is known as iterative 
deepening. It will be appreciated that the best 
move so far found is always available, and 
machines using this technique generally 
display this best-move-yet — a feature which I 
have emulated in End- Game. 

Many chess computers employ an adjustable 
timer which will interrupt the machine and 
display the best- move-yet as its move — 
examples include the Super System II] — 
while others carry the process to its logical 
conclusion — examples are Sargon 2.5 and 
End-Game. 

Because of the time restrictions imposed by 
interpreted Basic, End- Game evaluates the 
material and strategic position for both sides 
just once. Captures and certain other strong 
moves are evaluated for material gains at a 
further two levels. 

The form of End-Game has been dictated by 
attempts to increase the speed. Constant 
calling of subroutines looks very pretty, but 
tends to slow execution time, while writing the 
same thing out several times is faster, but uses 
far more memory. I have stacked the most 
commonly-used subroutines at the head of the 
program to speed up their location when 
called, 

The greatest retardation of any Basic 
program is caused by the dreaded If statement. 
When this occurs in a loop, the loss of time 
accelerates rapidly- The evaluation function is 
called after every potential move, yet If 
statements are essential in it if it is to serve any 
useful purpose. I have moved some of the 
evaluation features from the main evaluation 
subroutine to reduce the number of times they 
arc called. 

It is interesting to see how careful selection 
of moves can reduce total thinking time for the 
machine. Lines 1 30-170 are called every time a 
pawn move is con&Jderd and should, one 
might think, stow the program compared with 
the speed of exception without these lines 
which test to see if advancing a pawn enables 
the opponent to snap it up immediately. 

After all, the second level of search will find 
that the pawn can be captured by a strong 
opponent move, so w r hy put it in? In fact, End- 
Game likes to advance pawns and so* by 
deterring an advance into the jaws of an 
opponent, a more sensible first move is put at 
the top of the list after the sort, 

Thereafter, alpha beta pruning does its work 
and the weak pawn advance is barely con- 
sidered instead of being fully evaluated as the 



Variables defined in program 


lines 1110-1120: 


CC * 0.012 CE = 1 CF - 02 CG 0.3 Ch i 10 


CJ=30CK^15CL = 50CM 


= 1GCO = 2CD-l 


C2 = 3 




i Malarial count: pawn = CD .. 


ng=CZ 


, Pawn moves; 




Do not approach enemy king 


-CG 


Do not approach enemy pawn — CG 


Stay off edge of board 


1 :CH 


Advance to rank V 


4 V J * CC 


Avoid having Y pawns on on* 


j 


fite 


-[Y-lfKYxCF 


Pawn advance: no opposition 


in first channel 




* CG 


to eighth rank 


+0.5 


score for first channel 


Material count /CH 


score for second channel 


MateriaUount/CM 


En passant threat 


-0,8 


King moves: 




King opposition 


+ CE 


King environment 


+ 1/CK, + 3/CK 


Avoid capture bv pawn 


-5 


Do not stray from centres 




squares 


+ 1/CJ 


King ripple 


Material 




count/ICGxCU 



TMfe & Evaluation table tor Sid* Game. 

first move on the list. This saves a great deal of 
time. Thus the nett effect of the time- 
consuming lines 130-170 is actually to 
accelerate the program. 

The evaluation features are listed in table L 
The variables which store the scores for 
different features, shown in table l> are all 
found in lines 1110 and 1120, and so can be 
altered if you feel like experimenting. 

Two features which I believe to be original 
are the pawn-advance routine — subroutine 
510 - and the king ripple - lines 22602290. 
Both are stored outside the main evaluation 
subroutine. 

The pawn-advance examines a three-square- 
wide channel ahead of the pawn after it has 
moved j all the way to the eighth rank. The 
move is scored according to whether the 
channel is obstructed — enemy piece in front, 
king scores high — or assisted — friendly piece 
in front s king scores high. The same channel is 
then examined again for its entire length, and 
again scored. 

The second score shows whether the 
advancing pawn has numerical supremacy 
over the opposition: that is, one of two pawns 
will be encouraged to advance if the path is 
blocked by only one enemy pawn. 

Obviously, this is a very crude evaluation 
feature, but it works relatively well for End^ 



Game while minimising the number of If 
statements required. 

The king ripple is a very low-scoring feature 
put Ln solely to prevent the king wandering 
aimlessly when most of the other material has 
been removed from the board- All the squares at 
a distance of two squares from the king, then 
three, then four and so on, are examined until 
another piece of either side has been found. The 
king [hen heads towards this piece, 

King ripple is time-consuming and is 
evaluated only for the computer's pieces. 
Coupled with the routine which weakly dis- 
courages the kins from wandering outside the 
central 1£ squares > it should prevent the king 
from becoming * 'lost" for too long. 

Kivif, environment searches each square 
within one move of the king, and scores 
favourably — +3/15 — for each enemy pawn so 
located and less favourably — + If] 5 — for each 
friendly pawn. Obviously, the two kings cannot 
approach each other, 

Other evaluation features include low scoring 
for pawns on either edge oft he board, avoidance 
of doubled pawns - trebled or quadrupled 
pawns are punished exponentially — an 
exponcniialty- increasing score as a pawn 
advances tothe eighth rank and encouragement 
for one king holding the opposition over the 
other. 

I have remembered End-Game's chess 
origins by not insisting thai [he machine 
advance a pawn to the eighth rank if a good 
move, such as a capture, exists elsewhere on the 
board. 

En passant has been catered for by a 
somewhat elementary method. If the human 
makes a move which enables the machine to 
capture ai passant, the capture h given priority 
and properly evaluated. However, the machine 
does not allow for t$ passant when otherwise 
evaluating moves: instead, the possibility of « 
passim is assigned a score of ''undesirable" 
without evaluating in depth, 

End-Game was written in standard Microsoft 
Basic with no Peeks or Poke. The use of cursor 
commands, including screen clear and home 
greatly improves display. 

Lines 1 310 and 1 770 operate a timer routine 
for my Sharp MZ-80K and can be adapted or 
ignored, Many computers do not like jumping 
from loops, which has influenced some of my 
program lines. Other Sharp users will require 
one of the Basic Extensions for the logical 
(continued on next page) 




HAH HAH 



Pawn advance. A shows 
first cframaf, 3 $&CQrt<f 



in 




°^ 



Pawn advance, The most 
fikefy move for biack wi/i 



King rippte. 



Aft Aft Aft 

A 8 C 

King envrronment. The most favoured 
position for ftfe king is C; tess favourable is 

8 and least favourable is A 



A starting position for 
games pr^-stored in 
frttf ■ Game. 



■ ■ 






■■*■* 






■'■*■ 






■aQnoa 







YOUR COMPUTER. DECEMBER 1981 31 



(continued from pr&wous pag*) 

operators And and Or in some lines and ihc 
string inequalities in others. 

Line 500 returns a value of—] for each 
bracket cd statement which b true, and if 
false. This line runs some 20 percent faster than 
the corresponding If statements would, 

Sadly, the program runs to 9 r 5K as it stands. 
This can be trimmed to 8K by removing the fast 
sort — this will slow it somewhat — by 
removing the screen-display lines, and by 
removing all but two of the data statements, 
together with the lines which select the data 
statements. 

Program Function Line 

Evaluation 240-400 

King erw iic n merit 4 1 -600 

Pawn advance 510-629 

Move storage 630-670 

Third-level captures 680^10 



Fourth- level captures 820 920 

Data statements 900-1040 

Variables defined for evaluation 1 1 1 0- 1 120 

Set-up position 1130-1280 

Fkst ply 1290-1640 

Second ply 1550 1760 

Move display 1770-1820 

Input moves 1B30-20S0 

King-move generator 2090 2310 

Pawn one-move generator 2320-2350 

Pawn two -move generator 236G 2450 

Pawn capture 2460 255G 

Fast sort 2560-2330 

Alpha-numeric conversion 2840-2370 

Screan dteplay 2880-3010 

End- Game has six difFerent games prestored 
in 12 DaEa siaLtmcms — the starting positions 
are shown in the diagrams. These can he 
scleccedj or the program will choose randomly 
between them. A display of the board is given — 
copy it on to your chess board. To set up your 



own p jsstion, it will be necessary to alter two 
Dal a statements. 

The machine will prompt 
YOUR MOVE 
when read, followed by 

FROM? 

It will now accept ordinary alpha-numeric 
entries, such as 

(FROM) D r 2 <TOI 0,4 

Alternatively, J yping P, 1 will give a display of 
the board which ss displayed only if you ask for 
it. Typing QJ will reveal w r hat the machine 
thinks your move should be and typing Y J will 
cause the machine to an on Us own suggestion 
for your nunc without need to enter it. 

The only error check run by the machine on 
your input is thai there is a piece of yours £i the 
point from which you are trying to move. Thus 
you can move pieces round both easily and 
illegally should you want to. 



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Drawing on examples from his 
program written for the Sinclair 
machines, Philip Joy shows 
you how to go about creating a 
chess game of your own. 

THE zx-w IS noi the best machine on which to 
wriw long And complex programs because of 
its Basic. There are hardware problems as well 
as software ones — a poor keyboard for 
entering code in quantity, and slow speed. The 
Bisk does not let you use two-dimensional 
arrays — which at first might seem a problem 
— because of an eight-by-eight board. 

However, it proves not to be t and in Fact it 
helped nie to such an ex cent thai I have kept a 
64 array for my ver&km for the ZX-8l 5 even 
though it has multi-dimensional arrays, By 
having integer arithmetic only, the troubles 
with many INTs were overcome. The main 
hardship is the feci that it did not have a really 
easy way to emcr machine code. Read or Data 
would have helped or even a monitor would 
have made the entry of machine code easier. 

As the program neared completion, it was 
structured around five main unii*: initially 
at ion, movement, poinis, player, and back up- 
Each one of these units has a specific use and 
place in the program. The movement was the 
mo*: difficult to write and proved to have a 
peal deal of bugs. The points section is the 
thinking part of the program and calculates the 
best moves: it was the easiest part to wi:u\ 

The player is the unit which keeps the user 
informed and sorts his moves for the computer 
to respond to. Back-up plays the greatest part 
in keeping the program working smoothly. It 



Writing chess 



finds, for example, the level of play, sorts the 
points and deals with the machine code. 

The computer obeys ihe laws of the game in 
a much more logical way than the average 
player might. If a good situation arises, a 
player might rush his next move and make 
either an illegal move, or one which could lead 
to hi* losing the game. If a computer obeys ihe 
laws of chess, checking lor such things as dis- 
covered rfteck, illegal castling, and general 
illegal piece move** it does mean ihat this 
clement of rush is removed. 

Most of the moves are straightforward or are 
mixtures of two simple moves, e.g., ihe 
queen's move. The bishop and the rook movc- 

Figwe I. How ths computer makes a mow, 



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I 
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L 



ments could be calculated by a person with 
some experience of computer programming. 
With some thought, the L-shaped knight 
movement and the queen's could be solved. 
However, the two pieces* the king and the 
pawn which move only one square at a time, 
U? ihe pieces with many conditions attached 
to them. These two pieces have many 
characteristics which, although are not 
directly connected with them, make the 
movement hard to perfect. 

The program is based around a 64 -character 
array which holds all the black and white 
pieces and the blank spaces. The program uses 
two vectors to search for its move. One is the 
horizontal vector, or the number of squares 
Jiuvn, while the vertical or the number of 
squares along is used as the other vector. To 
look into the array, these two vectors are 
brought together by the equation 

{x-1)*8+y 
to give the square about which we want to find 
some information. Our points tabic is scanned 
for a move,, and this move is then tried. If the 
move fails, it is given a value of in the points 
table to prevent its being tried again, When a 
move is found, the array is updated, and the 
board is printed for the player's turn. In any 
move i the important thing to remember is that 
i he moving of a piece can cause check, or 
checkmate. Many human players could over- 
look this part of ihe game. 

(continued on rwxt page} 



YOUR COMPUTER, DECEMBER 1981 33 



(continued from previous page* 

After each move, the computer will discover 
whether its king is in check, ir it is, the 
position is restored arid another move tried. If 
the same directions for a piece were Tried in 
the same sequence ei'ery time, the bishop, for 
example* would always move upward* and 
left. The computer must, i here/ore, iry 
different directions in 3 different order each 
lime. 

Difficult decisions 

The initialisation stage is the section where 
the most difficult decisions are made. For 
example, you have to choose the form of 
storage, the arrays and their sizes and the 
different variables. The representation of the 
pieces and the style of play will all be affected 
by the way you decide. Ii is also here where 
you can include le;nur*s which arc noi needed 
or could be combined to reduce space, and 
time. 

The movement of the pieces is the only part 
of the program which has been heavily flow- 
charted. It is logical and is a part humans do 
not consider in great detail — hence the danger 
of bugs. It took aboul a month to remove the 
bugs in this section, mostly by trial and error. 

We search for a possible move by working 
across the board and using our memory to 
decide whether a piece can move or not. The 
computer discovers a move by trial and error, 
Wc must also be careful to take into account 
that the program could be faced with a 
situation for which it cannot find a move. In 
this position, the computer u ill have to decide 
whether it is checkmate or stalemate. 

The pawn was the easiest to tackle with its 
one move forward or two if it was on its first 
move. All you have to do is to subtract from 
the horizontal vector and check whether the 
piece can move to this square. If ii is on row 7 
or row 2 depending on colour, we can lake two 
from the horizontal vector, However, before 
we move we can check whether a diagonal — 
found by adding or subtracting one from both 
the vectors, depending on which way you are 
going — is occupied by an enemy piece, Ifit is, 
we would take it if it does not put the 
computer's king in check. The only problem 
with the pawn arises when ii is about to check 
— it has two possible moves. 

The bishop and the rook are roughly the 
same. They created no problems and took very 
little time to develop. For a rook s we add one 
to the file or row depending on which 
direction it is moving. The bishop is slightly 
more difficult azt it has to add or subtract one 
from the fib and row — again depending on 
which w T ay it was moving, When wc have 
found our new position, and before wc make it 
on The board, we check for a number of thmp. 

Complicated pieces 

First, we see wticthcr it has reached the 
other side, or whether it ha? reached a piece of 
its own colour. In either case, we know that 
this is as far as it can go. If ii reaches an 
opponent's piece, it can replace it with its own 
colour and subtract one from the number of 
pieces the opponent has on the board. We 
must also check for a check or checkmate and 
if there is one, we must cither move it to 
another square or not move that piece at all. 



The knight > although it may seem a compli- 
cated piece, is very similar to the rook and 
bishop. You add two to one direct ion and take 
one from the other, or any other combination 
and you must remember that this piece only 
moves once > unlike the rook- There are in fact 
eight moves a knight can make snd you must 
check for the piece going off the board. 

The king can move in any direction but only 
one nqujre at J tunc. *o you can see hgw easy it 
is to cater for it in the program. We must 
remember, however* that it is the piece which 
must not be attacked . We have to find out 
whether it is in check both at the beginning, 
and at the end. 

The way this is done is to search along every 
diagonal, file and row until we meet an edge or 
a piece of the same colour. If this happens, 
move on to the next path because the king is 
not being attacked in thai direction. A simple 
For-Ncjci loop will deal with that. 

However^ it wc find an opponent's piece we 
must discover which piece it is since all pieces, 
apart from the queen, are limited in their 
directions of attack. If the piece is not an 
attacker, wc can consider knight moves away 



Element 


Value 


Comments 


number 






1 





piece either not present 
or has been tried 


2 


540 


3 pawn on its Starting 
square 


3 


600 


a queen being attacked 


4 


539 


a pawn being attacked 


5 


450 


a bishop in the middle, 
not being attacked 


6 


460 


a castle on its starting 
square 


7 


440 


a pawn 


s 


440 


a pawn 


9 


443 


a pawn - a random 
number is added to make 
sure each game £ 
different 


10 


610 


a knight in a poor 
position 


11 


S80 


a knighi being ettecMd 


12 


340 


the king 


13 





a piece already tried 


14 


508 


a bishop in a poor 
position 


IB 


570 


a pawn on the square 
before it is promoted 


16 





a piece already tried 



Table ?. Points fatte with fist of pieces. 

from the king to see if they contain a knight of 
the opposite colour. If we do not find check 
then we can move on. 

If we fmd check, wc have the other problem 
of discovering whether ii is checkmate. The 
three ways of eluding check arc moving the 
king, taking the attacking piece, or blocking. 
The first is the easiest — move the king to all 
the possible position* and verify io see if the 
king is in check. If he is not in check* the 
situation has been solved. 

The next option — taking the attacker — is a 
far more diflkult problem io solve. We must 
use ihc samp routine to see if any piece is 
attacking. If it b, wc can move it to take the 
attacker and, as long as wc do not cause 
another check or double check, we have again 
solved the situation. 

Blocking a check with a piece is the most 
difficult aspect. We can first see if the attacker 



is a knight, because if ii is we cannot block. If 
it is not, we must, using a Far-Next loop, go 
from every square between the king and the 
attacker and see if any one of those squares is 
a i tacked by tuic ot its uwfl pieces. Ifit is, we 
can move the piece co block the attacker. 

This again ha$ two conditions, the first is 
that it is not a double attack, and the second 
that it doe* not create a disc ove red check. If 
you still can noj find a way out, the computer 
is in checkmate, and you should have it sav so. 

The part which decides how well a computer 
plays is its points table. Each program has its 
own points' table and a different way of filling 

The points table is made up of 16 elements, 
and each cfcmen* is initially given 500 points. 
The computer then goes through the board 
until it finds one of its pieces; it then stops and 
evaluates the position. It does this by looking 
ai which piece ii Ls And subtract* points if it 
does nut want to move it. 

Skill of the game 

For example, it is much safer io ninve a 
bishop than a queen. Th-j \Kr-\ a\\\ tviiM In - 
other aspects such as whether it is being 
attacked. I fit is, it will have to move the piece 
concerned so some points will need adding. 
Then it can ]nnk it its position; ifit is in the 
centre, points will be deducted so that it is less 
likely to move. Other considerations can be 
evaluated, depending on how good a game you 
wish to play, and how much space you have. 
When this points table h built up, the 
element with the most points will be tested to 
see ifit can be moved, Ifit cannot then a zero 
will be placed in it so that h will not be tested 
again. 

The element with the most points moves 
first, The skill and standard of the game 
depends so much on this pari of the game that 
to make it play better, a great deal of work on 
this section is needed. The results we obtain 
from a points [j hie deed noc be accurate 
enough for playing against some players, but it 
cart be a match for average players ifit is dealt 
with correctly. 

The player section is the pan which will 
interact with the player $o that he can enter his 
moves and can see the board- My program dis- 
plays a full board with the pieces represented 
as letters: 

Kinf)-K. Queen-Q, Rook-C i Bishop B, Knight N r 
and Pawn-P. 

This is satisfactory for a ZX-80 but if your 
computer has graphics, or else a user+defmablc 
character set, then use the letters. The normal 
way for entering chess programs into a 
computer such as a Chess Challenger is by 
algebraic methods. That is used here — it is 
also the chess standard. 

The final section of the game is the back-up 
which is (list a a^Luv'um uf amurics which 
will deal with such things as: 

■Set up points table 

■ Zeroing of moves a I ready tried 

■ Loading and using machine code if any is 
present . 

■ Reprinting board. 

■ Putting pieces on the board. 

■ Different board set-ups — black or white. 

■ Other tasks which can be u$ed by all Of tfirj 
routines already mentioned. 



34 YOUR COMPUTER, DECEMBER 1381 



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YOUR COMPUTER , DECEMBER 1381 35 



SOUND VIEWS 

IN TUNE WITH TANDY 




Alun Evans' nine assorted — 
and easily converted — Basic 
and assembler routines are 
designed to reveal the musical 
side of the TRS-80's nature. 
The sound effects they 
produce can also be used to 
improve the games you play. 

Once yqi; have added sound effects to a 
computer game, you will probably be loathe to 
play games which lack them. With a little skill 

chu TRS-80 tan be induced to gloop and 
gurgle like the very best arcade Space invaders 
and can he made to play uines and to respond 
to The keyboard like a simple electronic organ. 
The bad news, for Basic fans, is thai ihe 
means to make sound* is through machine- 
code programs. Before you abandon hope, 
however* take heart: t have supplied the data 




Figures Is end Jb. 

that sets up the machine code so that the 
routines can be Poked into the top memory 
and accessed from Basic. 

Those who understand assembly language 
will find some suggestions for further 
refinements of the routines so chat they can be 
more widely used, 

Sound, a simple pure nose, is a sine wave — 
figure 1. The pitch of the note is a function of 
the rate at which the cycles arc produced. The 
more cycles produced in a given time, the 
higher the pitch of the note. Figure ta shows a 
note which has a higher pitch — more cycles 
— than the noEe in figure lb. The Juration of 
the note is the length of lime wc allow a 
particular rate of cycles to be produced. 

It is these two variables,, Pitch and Duration^ 
which we shall have to control when we mate 
sounds with the computer. 

Sound is generated in the cassette interface 
which watches bits and I at port 255, The 
since wave of a simple note is approximated tOj 
in the TRS-SQ t as shown in figure 2. We set 
port 255 to I, hoJd it at 1 and then reset it to 2. 
If we keep doing this we end up with a square 
wave- Form. 

The length of time we hold the port in either 
si ate is shown as "f \ Clearly, the longer we 
make "V\ the fewer cycles we shall be able to 
complete in a given time. Hence the longer 
"f" is, the lower the pitch of the note. 
Similarly, we raise the pitch bv shortening 

In the Radio Shack- published TRS-80 

Assembly-Language Programming by Bardcru 



there is a simple assembler program which 
enables us to product square waves and which 
giv« u& control over both pitch and duration 
of the note, 

However, before we sian on the production 
of some sound-making code, we must set the 
machine so that we can hear what we are 
doing. Connect the larger of the two grey [ack- 
plugs which normally plug into the 
computer's CTR into the input socket of an 
amplifier. I use an old Sanyo cassette radio 
recorder, plugging into the microphone 
socket, 

I then put a dummy tape into the machine, 
set it lo record, and hear the computer via the 1 
recorder's monitoring facilities. Remember to 
replace the jack- plug into the computer- 
controlled CTR before attempting any 
CSaving — or you will finish with a blank 

tape. 

Now let us examine Hardens routine — 

listing 1. Notice thai zero values are given for 
both pitch and duration. This is because they 
will be Poked inio the routine from Bask, 

Listing 2 shows the Basic which will let you 
experiment with tones produced by the 
machine code. All you obtain at this stage is a 
single tone repeated 10 limes. However, if you 
keep a record of the numbers you have tried, 
you begin to develop a fed for the kind of 
noise to expect from various values, 

Experimenting with listing 2 should show 
you that the relationship between the duration 
of a note and its pitch is a complex one. If you 
hold the value for duration constant and vary 
the piteb, you will set that the higher notes 
play for less time than the lower ones. 

Even such rudimentary sound facilities have 
their uses. Listing 3 demonstrates just how 
easy it would be to make your favourite games 
more lively. Xoie that there is no need to 



ftjrtrtl 


I — — : I 


JVr.i- 2 



Fjffur* 2. 

repeat the Mem Size fix or the lines that Poke 

in the machine code unless the computer has 

been turned oft" between programs. 
The nest step is to experiment with tunes 

scored in data lines. This is what the listing 4 
do« r Once again, repeat only lines 10-60 from 
listing 1 if you have corrupted any of ihe 
contents of the protected memory space 

Saving the musical data as an array, as in 
lines 90-110, has two advantages. First* it 
avoids the need to reread r he data if we want to 
play the tune more than once. Do not forget 
that Restore would reactivate all data in a 
program, not just the piece we want. 
Secondly, it makes it possible to rearrange the i 



order in which the noies are played. Delete 
lines HlMSO ffO®) the limine 4 mi ddd liiClBg 
5. The computer is now composing^ and 
playing, its own tunes. 

To make the computer into a simple organ, 
we need a program ;hat watches the keyboard 
for key-pushes j and which then supplies pitch 
values to the sound -ma king routines. InkeyS 
would do this but that uould supply only a 
onc-dfTbur^: «.■: vu:::J - no bad thing if you 
wanted an audio response to be given to the 
user but not wha; we want for the organ. 
Better for our purposes would be to Peek the 
keyboard, 

The TRS-80s operating system locates the 
number keys 0-7 ji address (244S, By Peeking 
this address ihe program can read wtikh of the 
keys is hein^ pressed, If 

PEEK '12448)- 1 
then the key is 0. If 

PEEK H244&* = 2 

Melody 

The sound of MZ-80K is 
something owners of the 
machine can enjoy without 
having to buy a costly sound- 
box. Bob Edwards reports. 

The SHAttt* &f24QK computer is remarkably 
versatile in many respects, For instance, k has 
a set of graphic* superior to most other 
computers in its range, Unlike some of its near 
competitors, most of the graphics are 
accessible directly from the keyboard — more 
than 104 shapes at ihe press of a key. 

Another way m which the MZ 80 K is uhead 
of its rivals is in its built-in music capability; 
there is no sound box to buy as an optional 
extra. A s.1 might forward statement >ueh as: 
10 Music* 61A1R4A1* AtC AR1 A3 F3RS" 
will give a passable rendering of the flrsi line 
of C&ioxef B&gty> Making this line into a string 
by replacing the word Music with MS "makes 
life even easier; 

20 MUSIC MS 
will make the machine play the entire phrase 
Using the same principle to produce single 
notes of varying length Gin provide the beeps 
and hoops [hat make computer game-playing 
that much more fun, 

This facility, especially when combined 
with the excellent graphics set, means you can 
create computer pmes which surpass those of 
other machines in the price ranee. The 
budding EectWens among ns Can compose 
tunes hi their heart's content and then bear 
them played bacSs at once. 



36 YOUR COMPUTER, DECEMBER 19B1 



. 



MAK3NG MUSIC 



then the key is 1 and so on up to a maximum 

PEEK (124481-128 
For key 7. 

Listing 6 is the Basic which wilt give you the 
Stylophoni! you always wanted. 

Assembly-language buffs will see that ii 
would be far more efficient and relatively 
simple to have the machine language watch 
the keyboard, rather than Basic The increase 
in speed should make it possible to watch all 
the keys and should remove the vibrato effect 
from the notes. 

Sound effects, laser cannon, flying saucers 
and the lite; all depend on the sound- making 
routine being supplied with a sequence of 
frequency values. Each oT these it plays for a 
very short duration and there should be no 
noticeable gap between the notes used. 

The machine* language routine we have been 
using so far has to return to Basic to find what, 
if any, values we want it to use next, This 
process is too slow to achieve the kinds of 
effects we want. 

The answer ii to rewrite the machine code 
so that she routine feeds itself from a block of 
data that we have set up for ii in advance. The 



assembler listing ii reproduced in listing 7. 

Basic programmers will Find this routine 
translated into Pokes in listing ti_ Before using 
the Bask though, look at figure 3. 

This shows the TRS-80 memory area where 
the new routine lie*. Notice ihat the data used 
by the routine — the frequencies we w r ill want 
it to play — lie immediately above the routine 
itself. If you want to use another set of notes, 
or want to try out sequences oT sounds you 
have invented, it is into this area, from 32489 
onwards, that you must Poke your data. 

Note, too, that all such sound sequences 
must end with a zero. It is the that turns off 
the sound and returns you to Basic. Omit it 
and you will probably have the humiliation of 
groping for the reset switch to obtain silence. 

Listing 9 offers some replacement sound 
sequences, In each case replace line 50 in 
listing 8, 

The important thing to realise when you 
begin to experiment with patterns of your own 
is that the duration value is fixed for the whole 
sequence. That means high-pitched notes will 
play for relatively much less time than the 
lower ones. 



As a counter measure to this, I have Ibund 
you need to pack the sequences with many 
high-frequency values decrementing slowly, 
while the deeper notes can be fewer in number 
and can make bigger jumps in value. You 
could create a table of duration values, and 





Figure 3- 




Figure 4. 


Y 
X 


n&tilirm *i 


324*7 

■."J'- u 
324&Q 


Cdfthcm Data 


^.\j\ mf \ .I't *♦■■ 




Dara lor 


i he 
Mating 0&i£ 









of 




distinction 



I use the line from Cohwi B$gty as the 
"You lose" music on a number of games. It is 
surprising how a relatively simple game can 
benefit by the addition of a few interesting 
noises — the player interest seems to increase 
by a factor of 10. 

The otherwise very good manual supplied 
with the MZ-80K fails to mention that the 
sound capability of the machine goes very 
much fun her than the Music statement k as 
anyone who has played the Sharp version of 
Spa.ce Invaders will know*. 

It is a reasonably easy matter to product a 
whole range of weird and wonderful noises 
and effects from a were-wolf to a wolf-whistle, 
from a telephone to a motorbike. With a 
galaxy of giiss$udi and space noises in 
between. 

The secret lies in two monitor subroutines 
and two memory locations which between 
them control the way the sound is generated. 
It is easy to access these from Basic via the 
Poke and USR instruct ions, 

The machine takes two numbers from one to 
255j which arc Poked into memory locations 
45 1 3 and 4514 and uses ehem to divide down 
ihe 2MHz clock which controls the CPU. 
Monitor subroutines are then used to start and 
stop the sound, These subroutines are called 
by L-SR(65) to start die sound and USR{71) to 
scop it. 

This may seem a little complicated but it is 
simple when you are used to it and it operates 
very much faster than the Music command of 
Basic. Combining all thb with For-Next loops 
means you can really begin to take control of 



the synthesiser and produce sounds that are 
limited only by your imagination. 

The best way to become acquainted with 
this facility is to experiment. Try the 
following short rout in us. 
10 FOR A- 256 TOO STEP -12 
20 POKE 4514,1: POKE 4S13,A 
30 USR168J: NEXT A: MUSIC "R2" 
40 FOR A - 255 TO 255 STEP 8 
50 B m ABSW: POKE 45l4,lr POKE 45l3 r B 
60USm68!:NEXTA; USRJ7I) 

That is how to produce a wolf-whistle. Try 
altering the values of A and see what happens 
to the sound. Note also in line 30 the use of 
Music "R2" in place of USR<7Ii Try 
switching them and note the difference. 

To produce a photon torpedo or laser gun 
you could base vour experiments on: 
10 FORT- ( TO 4: FOR A- 1 TO 150 
20 POKE4S14.A- USR(68>: NEXT A 
30USRI71): NEXT T 
That is even simpler than ir looks. The For- 
Next loop of T determines how many times 
the gun is fired. The actual program for the 
effect will fit on one line. Again, try altering 
the value of A and see what happens. Replace 
the USR{71) with Music "R2 M and note the 
effect on the gap between the shots, 

Music "Rx" where x is a value from to 9 is 
another way of stopping the sound but does 
have a different effect depending on the value 
ofx, 

A Trimphone^type telephone might find an 
application in a program: 

10 FOR A * 1 TO 3: FOR B = 1 TO 2 
20 POKE 4514 J: FOR C- 1 TO 15 
30 POKE 4513,150; USR(68) 



40 FOR D- 1 TO 6; NEXT D 
50 POKE 4513,256: USR<68! 
60FORE= 1 TO 6: NEXT E 
70 NEXT C: MUSIC "RT 
80 NEXT B: MUSIC 'Rr : NEXT A 

This routine will also supply the ringing tone 
and the engaged tone by altering the values in 
lines 20,. 30 and 50. This is a good routine 
with which to experiment by altering all the 
values and noting ihe effect . Note once again 
the use of Music 4, Rx" in place of USR(7I); 
exchange them just to see what happens. 

The programs for different rounds arc quite 
similar to each other which makes is possible, 
for instance, to have only one subroutine in a 
program but obtain several sound effects from 
it merely by altering the values of the variables 
when ihe routine is called. 

1 hiive written a short program to demon- 
strate some of Ehc sound* available from the 
MZ-80K and to show how to go about 
achieving them. Anyone who cares to send me 
"ik nf their programs und an SAE for the 
return of ihe cassette is welcome to a copy. 
The address to write to is 95 Bowring Park 
Avenue, Liverpool L16, 

[f you have ever played ihe game of Star 
Chess you will be familiar with the "Game 
won' 1 noise; this produces something similar: 

5FORT= 1 TO 5 
10 FOR A 10 TO! STEP -1 
20 POKE 45KA 
30FORB= TO 255 STEP A 
40 POK£45l3 r B: USR<68> 
50 NEXT B, A: USR(71| 
60 NEXT T 



YOU A COMPUTER. DECEMBER 1381 37 



{continued from previous page) 
maintain a duration tabic pointer at machine- 
code level - 

The problem our program has is that it can 
cope with only one set of sounJ-eFFtas daca. IF 
in li i^iiztu: we wanted several different effects 
we would have the slow job of Poking each 
sound sequence into memory before we could 
hear it. 

It would be much belter to have a situation 
in which we could si ore all the sounds in 
advance and then tell the sound- maker where 
to find the set we wanted at any time. 

The machine code knows where to look for 
ihe sequence of notes we want it to play 
because it is given the address at which this 
data starts, Ae the moment, the routine looks 
at addruss 32489, Suppose we had several 
blocks of data, as in figure 4, each stacked 
above the other. All we need to do is feed 
address * h x" u> the routine u> hear she Jiving: 
saucer s address "y" to hear the laser gun. 

The complication is that the machine-code 
routine cannot accept a whole address. The 
address must be split into two bytes, called the 



most- and the least-significant bytes respec- 
tively - MSB and LSB, 

The mathematics to calculate these values 
for any address is not dsllkuiu and the 
computer will crunch the numbers for you. If 
N is chu address, then 

MSB =INTfW2«) 

LSB = N-(MSB ' 256) 

Now we have our stacked sound effects, we 
have the addresses at which ihev si an 
converting into an MSB and L SB. All we need 
to know now is how to convey this 
information to the sound-making routine. 

This, at least, is simple enough. You need 
the LSB in the second byte of the routine, and 
the MSB in the third byte. Yoy can amend ihe 
airreni Basic program by inserting the 
following just before making the L-SR call: 
POKE 32459, LSB: POKE 32460, MSB ; 

You can alter the MSB and LSB as much as 
you like but they must always go into the third 
and second bytes of the machine^code routine. 
You can even try putting some ROM 
addresses there. The computer will then make 
music from iis own ROMs until it hits a zero. 



Assembly- language programmers will have 
realised that a major weakness of the routine 
we are using to generate ihe sound is that 
while she sound is playing, the CPU bothers 
about nothing else. Most of the lime it sits, 
gently contemplating m Nor gates, waiting 
for the B regisier to go aero, as in lines like 
LOOP DJNZ LOOP 

This means that a graphics-orientated game 
would not receive any screen updates while 
[lie sound was playing, A solution might be to 
replace the simple idea of consuming time by 
decrementing a register. Set the port io 1 or 2 
and then check and update the board. You 
CO u id con'rol the time, .ind hence the 
frequency of the sound by controlling the 
number of T-states yotir screen check 
involved, 

Those :r:t nailed by the use of assembly 
language and who want to know more about 
the subject could do worse than buy Barden's 
book. DespLte us relentlessly cheery approach, 
it is as gentle an introduction to assembly 
language as any 1 have read and a good deal 
cheaper than most. H 



LOOP! 



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^ - 48 

[1 - ;.:■■ 

d- a? 

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■ ! A*3 - F 
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S1N0 



LOOP I 



L0OP2 



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LI' 

LD 

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OUT 

DJHZ 

LD 

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3S YOUR COWlPUTefl, DECEMBER 1961 



lire 

Essential 

loft ware Company 





THIS IS NOT A 
PRACTICE DRILL ! EARTH 
IS BEING INVADED 
ONY0UR TR580& V^ |E 

Galaxy Invasion 




The newest and most exciting invaders 
type game yet! Cruel and crafty aliens 
attack Earth r You are the sole defender. 
As you fire your laser at the aliens 
they swoop down and bomb you, 
Exciting use of graphics! Must be seen. 

TRS80LeveM&H16KTape 
Video Genie TGK Tape 

SuperNOVA 





Attack Force 

Dodge the alien Ramships and fire 
missiles to destroy them before they get 
you. The alien Flagship uses his deadly 
laser boll to transform a Rarnship into 
another Flagship or into your ship's 
double Lookout! Destroy your double 
and you could destroy yourself. 
TRS80 Level I &H16K Tape 
Video Genie EG3003 1 6K Tape 



WJlMd 



Mow the amazing ASTEROIDS arcade 
game for your TRS 80! Your ship is 
floating in the middle of an asteroid belt 1 
Your only escape is to destroy them and 
the crafty alien spacecraft! Blast them 
with your laser, thrust, rotate or hit 
hyperspace to survive I 

TRS 80 Levels I & If 1GK Tape 
Video Genie 16 K Tape 



Cosmic Fighter 

Your fighter appears below a convoy of 
Aliens! If you destroy them another set 
appears who seem to be slightly cleverer 
than before! Soon your space station 
nea rs but before you can dock the station 
comes under attack! Survival te up to you I 
The excitement is just beginning 

TRS 80 Levels I & 111 6K Tape 

Video Genie 16K Tape 



qobblc 






Robot Attack 



TRS BO Levels I & II 16 K Tape 
Video Genie 16 K Tap** 
The Newest and Most Astounding Arcade 
Game thai TALKS has just Reached Planet 
Earth. Vou can't heslp yourself You have to 
stop therm at aJJ cost, Don't let up. Written 
especially for high Quality graphics you'll 
Sim pi/ be dajc&d and excited by tha acrfon. 



Watch out behind you! 
As you hurry through 
the maze collecting 
your energy 




modules y ou score points. But don't let t 
Gobblemen calch you If you are cralfy. 
sneek up behind them and neutralise them 
to gain exira points. Just keep a watch. 
When ihey attack you they come in fast. 
Jus I don't lose your nerve. 

TRS 30 Levels I & II 16 K Tape 

Video Genie 16 K Tape 



3-D means that as you wander througVYthe mai£s and buiidmgs .yy | 

full e/ 1 r£td rt. orar'ihfcr'rfHi-er'il.au- m nct^intlu en fxwiz vrt.i 1 i* PirtC 1 I i.rt n in ^ ^^^LB I "• 



full screen graphic display constantly shows your position in a 
perspective format as though you were actually therfel This "ral^s 
eye view adds an entirely new dimension to adventure- 
English language commands can be entered at any time to manipu- 
late your environment. The command sets are extensive and sophisti- 
cated. Dozens of objects are scattered throughout the mazes and 
buildings. You can pick them tip, burn them, throw them, etc. You 
may need the sword to fight ofr an ugly little man. Or a steel rod to 
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of Video Genie £329 + VAT 



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40 VOUR COMPUTER. DECEMBER 1961 



ZX-81 strings unravel 
knotty storage problems 



Strings and their allied 
functions constitute a valuable 
armoury for users of any 
machine who wish to write 
elegant Basic. For the ZX-81, 
with its relatively low storage 
threshold, these powerful 
techniques are vital. Graham 
Thomson explains. 

A ZX^i with it K KAM h a usefttl little 
machine. Among the most attractive facilities 
of its Basic is the string array used in 
conjunction with ihe functions Code and 
CHRS and the slicing operator. To. Some 
powerful programming techniques can be 
implemented with these tools — and you do 
not need to have recount to assembly 
language. 

Most Basics will have equivalent tunc: ions, 
so the techniques I shall discuss should be 
generally applicable. The particular array used 
is that declared lis;, for example: 
10 DIM S$(2000J 

Unlike the undeclared string, the S$ defined 
has the very useful property thai its length 



III EfllFf 



Zrtd tnm 



T 



Lintfh o^f word 2 

UHt nwiriw io OOTO a bfh WFiny) 
ChiucTfi fli wort 1 m 

Lonqlli o* »V^ 1 
V 
LWw no. to GOTO {£-byiM bmpfji 



never varies, We cart, therefore, access the 
individual bytes at random using, e.g., 

' S&ill or S$(l TO J) 
for both reference and assignment. In 
particular, we can maintain a simple numeric 
variable, say. NFB* which points to the u next 
free byte" in SS. Obviously, we set this to one 
initially and as we add to SS, we can increment 
NFB. For example; 

200 LET SSINFB TO NFB- 1 * LEN A$k - AS 

210 LET NFB NFB - LEN M 
adds AS into SS at the next free post I ion » and 
adjusts the next fret-byte pointer. It is true 
that you can achieve the same effect with an 
undeclared SS: 

300 LET SS = S$ + A$ 
I he easiest way, as so often, has 
disadvantages. 

Firstly, in many Basics line 300 will be 
l'\ touted by construciing :\ shadow copy ofSS, 



1 23456789 10 1112 1$ - - * * - » * S6 



SB 



B 



6 



NFB = 56, points herd 
v 

Characters of word 2 
V 

Length of Word 2 {binary) 



Characters of word 1 



Length of word 1 (binary) 



figure J. 

so that for a time there are two copies 
occupying precious space m your RAM. Thai 
h acceptable ifSS is short, but what about an 
SS that is 1,000 or 2,000 characters? Secondly, 
the easy way does not work with the more 
complex structures I shall outline. In the 
ft) [lowing examples p assume SS declared ?& 
before and NFB initialised so one. 

Now whai might we want to store in this 
st ring* and -pointer structure? An obvious 
starting example is a list ol words — such as 
you might want in that good old djssu: 
Hangman, A very simple piece of code to 
construct such a list is: 
90 LET NW-0 
100 INPUT A* 

110 IF A*- "END" THEN GOTO 170 
120 LET SfrlNFBl - CHRS LEN AS 
130 LET S$(NFB + 1 TO NFB + LEN 

ASI-AS 
140 LET NFB - NFB- 1 + LEN AS 
ISO LET NW-NW+1 
tOO GOTO 100 
170., . 
This builds a list of words in SS Each word 
is preceded by one byte containing, as an 
eight-bit binary number, the number of 
characters in the word. The variable NW 
counts the number of words. 

Obviously, one would like to refine the codr 
to ensure that no attempt is made co ex (end (he 
lis.c beyond the end of SS, I find it helps to 
draw simple diagrams of the structures bein^ 
built in strings — figure 1 shows how the 
simple list of words appears in SS. 

To pick words from the list — choosing, say, 
the next word in Hangman — we can count 
along using the length bytes to skip over 
words. For example: 
400 LET N~ INT tRND*NW+1| 
410LETP-1 
420LETN = N^1 
430IFN = THEN GOTO 460 
440 LET P * P + 1 * CODE SS|P> 



450 GOTO 420 

460 LET A* *• StlP + 1 TO P + CODE S$tP» 

470 ., . 

The code sets AS to the Nth word in the list, 
where S is created as a random number 
between 1 and NW t i he number of words. Note 
how the variable P hop* along SS always 
pointing jo one of the length bytes. This type of 
sequential search can take several seconds on a 
ZX'S 1 if you have a lonp list of, ray, 200 words. 

The general principle which we have seen is 
thai we can form in a single string, a set of lisf 
etiifiuK which constitute a simple list, This 
particular list tntrv had two components or 
"fields 1 *: 

■ Field 1 was one dyte long and contained the 
length of field 2. 

■ Fielrf 2 was Of variable length and contained a 
word. 

We can expand on t h is I heme a nd add furt her 
fields to form more complex list entries. For 
example* we can add a two-byte field containing 
a line number. This gives us the type ol" list 
which can be employed to control a program 
using single* word, English commands, Figure 
2 shows this type of list entry. Lists of thb type, 
where there arc several fields, are common I v 
called "tables". 

The code to build this kind of control iablc 
could be^ 

30 PRINT "WORD?" 

40 INPUT W$ 

60 IF WS - "END" THEN GOTO 150 

60 PRINT 'LINE NO. r 

70 INPUT L 

80LETA = INT[L/256t 

90 LET S$(NFB> ■ CHR* A 
: ■ >: ■ . i I S">\F^ li CHRSjL 2S6'AJ 
n0LETS$(NFB + 2)^ CHR$LEN W$ 
l20LETS$(NFB-3TONFB-2+ LEN 

W$} = WS 
130 LET NFB = NFB + 3+ LEN W$ 
140 GOTO 30 



150 



f continued on next paye } 



VOUR COMPyTEH. DECEMBER 138T 41 



f continued from pf&vrQus p&gei 

Line* 80 to 100 convert the line number, L, to a 

16-bii binary number stored in the first two 

bytes of 1 Able entry. The code used to control 

such a table might be: 

200 PRINT -WHAT NEXT?" 

210 INPUT A$ 

220LETP-1 

230 LET L« LENA* 

240 IF L<> CODE $$IP i 2) THEN GOTO 260 

250 tF S$IP + 3 TO P + 2 + L}- A* THEN GOTO 

300 
2fi0LETP = P + 3+ CODESS(P+2t 
270 IF KNFB THEN GOTO 240 
280 PRINT -I DO NOT UNDERSTAND" 
290 GOTO 200 
300 LET X 256" CODE S${PJ- CODE 

SWP+11 
310 GOTO X 

Obviously p the line number extracted from 
The entry at line 300 would start the code to 
process whatever word was typed. Building 
control tables and lists can save space in your 
RAM if you are writing complex program*. 

Other examples of uses of lists and lables are 
in storing the co-ordinates of plot points to 




TftmearuMftNTiutEj 



Figu/e J. 

draw diagrams or sections of diagrams. 1 have 
used this to store the plot points to draw the 10 
separate stages of the Hangman plcttm The 
list entry consisted of a one-byte count of plot 
points IulLiwuJ by i\us byses for each point - 
one X oo-ordinate^ one Y co-ordinate. There 
were^ of course, 10 such entries. 

In a. similar example, I wanted to draw large 
characters on the TV screen, specifically the 
digits to 9 and the characters fcL f ", "— w , and 
"-" The characters were drawn using a four- 
by-seven grid of plot points, and each table 
entry included a count of plot points followed 
by [heir co-ordinates. 

In fact a these were co-ordinates within the 
four-byscven grid, so that the program could 
draw the large character anywhere on the 
screen by adding the full screen co-ordinates of 
the bottom-left corner of the character grid lo 
the plot- point co-ordinate from ihe table. 

It can be useful io keep a separate array of 
poiniets io ihe table or list entries. It means you 
can construct a numeric array PTRS such that 
PTRS(1) gives the index into SS of ihe hh entry 
in the list or tabic. Naturally, if your list entries 
are all the same fixed Length* you can calculate 
directly the index to the hh entry, 

In ZX-8J Basic such a pointer array requires 
five bytes per element. If you were particularly 
short on RAM> you might use another string* 
PS> with pairs of bytes holding a 16-bit binary 
numbers as indices into SS. 



So the inde^ of the Ith table entry is SS would 
be 

25€* CODE P*(2 # l) + CODE P*<2+l*1) 

This is one of the situations where you need 
Lo consider whether or not the space saved by 
using a complicated string- based pointer 
system is wasted because of the extra prop-am 
code needed to use it. 

An interesting and often useful variation of 
the list or [able concept is the chain or linked 
Jisi, Here, one ofthe fields — usually the first — 
in each entry is, in faci > a pointer to the next 
entry. A simple example is a linked list of 
words. 

The entries look just like figure 2>exccpl that 
instead of a line number, the firsl two bytes of 
each entry hold the index to l he next entry. A 
very obvious use of such a linked structure is in 
sorting Ibts, To sort the words in our example, 
there Ls no need to physically reorder the list 
entries — we just swap the pointers. 

The use of such linked lists usually requires a 
separate variable to hold ihe index to ihe first 
entry of the chain, This variable is commonly 
called the head-of-chain pointer* Similarly, it is 
often useful to have another variable pointing 
to the East entry on the chain — the iail»of*cham 
pointer The last entry on ihe chain usually has 
aero in the next-entry pointer. 

A useful example of linked lists is a simple 
name and address program, The entries used 
have the format shown in figure 3, The 
following program code illustrates how this 
type of linked list can be manipulated. 

It is a set of subroutines to request a complete 
name and address from the terminal. Add it into 
the string SS at the next free byte, NFB> and 
adjust the links so that the list is maintained in 
alphabetical order of surname, irrespective of 
initials. 

For convenience, the hcad-of-ehain pointer is 
the first two bytes of the array SS, The sub- 
routine at line 1600 prints all the names and 
addresses in alphabetical order by following ihe 
chain of pointers. On the firsl use of the 
subroutine at line 1000, KFB is 3, and the first 
two bytes of SS are binary zero — space 
characters on ZX-8L 

1000 REM Sue R. TO ADD AN ADDRESS 

1010 CIS 

1020LET PNEW-NFB 

1030 LET SH NFS TO NFB + II - " " 

1040LETNFB-NFB + 2 

1050 PRINT "SURNAME? -1 

ToeoGOSua^wQ 

1070 PRINT INITIALS?" 

1080 GO-SUB 1500 

1090 PRINT "HOW MANY ADDRESS LINES? 

1100 INPUT N 

1110 LET SSI NFS) ^CHRSN 

1l2CLrr NFB^NFB + ! 

1130 FOR 1*1 TON 

1140 PRINT "LINE p, :l 

115OGOSUB1S00 

1160 NEXT I 

1 170 REM NOW LINK IT IN CHAIN 

1180 LET LP =1 

1 190 LET P-256' CODE S*l LP) + CODE 

S*OP+1> 
1200 IF P = THEN GOTO 1280 
l2l0LETAS = 5$tP+2) 
1220 IF A*>SSlPNEW + 2) THEN LET 

A* = SStPNEW+2) 
1230 LET L- CODE AS* 2 
1240 IF S*(PNEW + 3 TO PNEW+ U 

< = S*(P-3 TO P 4 LJ THEM GOTO 1270 
1250 LET LP =P 



1260 GOTO 1190 

1270 LET SSIPNEW TO FNEW + II = S*ILP TO 

LP*1) 
1293 LET A = INT IPNEW 2S6J 
1290LETSKLPTOLP+lt= CHR$A- 

CHR5<PNEW-256-Al 
1300 RETURN 

1500 REM SUBR TO INPUT A LINE 

1510 INPUT AS 

1520 LET L-LEN A$ 

1530 LET S$(NFBI^ CHR$ L 

1540 LET S$(NFB + 1 TONFB + LI-A$ 

1550 LET NFB- NFS 4 L + 1 

1560 RETURN 

1600 REM SUBR PRINT ALL NAMES AND 

ADDRESSES 
1610 LET P=l 
1620 LET P = 256' CODE StfFH 

CODES$tP + 1l 
1630 IF P-0 THEN RETURN 
1640 LET PT^P^2 
1650GOSU6 1800 
1660 LET B$ = A& 
167OGOSUB18O0 
1680 SCROLL 
1690 PRINT A$r ";B* 
1700 LET N = CODES$(PTI 
1710 LET PT = PT-1 
1720 FOR I = 1 TO N 
1730GOSUB 1800 
1740 SCROLL 
T75Q PRINT A$ 
1760 NEXT I 
1770 SCROLL 
17B0 PRINT 
1790 GOTO 1620 

1800 REM SUBR SET AS - LINE AT FT 
1610 LET L= CODES$(PTl 

1S2QLET AS$S<PT+I TO PT + LJ 
1330 LET PT=PT + L + 1 
1B40 RETURN 

Occasionally , it is even useful to create a 
double- Linked chain. There, each entry con- 
tains two pointer fields; one io the near entry* 
one to the preceding entry. With such a chain 
you can proem both forwards and backwards. 
It is often the case that an entry in a chain or 
list consists of several fields, some of which are 
H\ed in length, oihers arc variable and need to 
be prefixed by a length byte. In general, it is 
convenient to group listed- length fields at ihe 
beginning of the entry, followed by ihe variable- 
length fields. 

Surprising as it may seen, the techniques 
used by writers of fundamental software — 
operating systems , compilers, interpreters — 
can be implemented in Basic. If you can think 
"pointers, lists* tabic* and chains 11 you can 
broaden the scope of your programming 
ability, 

I have recently used all these technique* in a 
general* pur pose Adventure program, k con* 
sists of the code to request descriptions of 
places — short description, long description, 
other places you reach by going north, south, 
casr, west, objects and special words. 

The place descriptions and linkages form a 
table » the object descriptions form chains. Each 
place entry has a head*of- chain pointer field 
from which will hang nil ofthe objects dropped 
at rhat place- 
Thus defining a new game for the children 
does not involve writing another program — 
just typing in the new place tod object 
descriptions, ■ 



42 YOL/R COMPUTER, DECEMBER 1M 




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44 YOUR COMPUTER. DECEMBER 1961 



School computers: some 
lessons to be learnt 



Eric Deeson reviews the 
problems and progress of 
educational computing. 

Wl- are-: now approaching the stage at which 
half of Britain'* secondary schools have 
computer power available. Even the number 
of primary schools with computing facilities is 
no longer negligible! 

A number of recent surveys shown in cable 
lj have attempted to discover just how many 
computers their dm in schools, but their 
results have been overtaken by the advent of 
Sinclair's ZX-8L Both the Commodore Vic 
and the eagerly- awaited Acorn,' 1 BBC machine 
are likely to have a significant impact on 
educational computing. 

The Government plan* to subsidise the 
purchase of micros for schools. It will pay half 
the cost of cither the Research Machines 
J8Q-Z or the AeornyBBC machine for schools 
which so far have no computer. This project 
has been much criticised on [he grounds that 
support for specific machines might be 
unwise. It is also feared chat schools which 
have shown little interest until now will 
continue to be inactive. 

The educational use of computers can be 
broken down into a number of categories: 
■ Computer awareness, to familiarise 

students with computers and their uses, 
■Computer studies, where the computers 

Figure t. Materia/ eveitebfe from a sJngte frame 
Of 9 typittt COm&ui$r-$$$itfe£} teaming 
program, 



PRINT 
WHAT IS": 

LETC'G 



LET C-C+1 

INPUT D 
PBrfrTTD 




TRY AGAIN 



PmNTANS* 

is a*g 



PftlfJT GOOPJ^CtEAR SCREEN] 



I 





CET 


CIS 


MUSE 


Commodore Pet 


276 


53 


579 


RML 380- Z 


429 


99 


702 


Tandy/Video Genie 


S3 


S 


125 


ZX80/S1 


— 


S 


87 


Apple/ ITT 


IIS 


25 


252 


Na&tom 


— 


- 


44 


Acorn Atom 


- 


— 


59 


CET: Council for Educational Technology. 

1980. 
CIS: Cambridge Learning Systems, January 

1981. 
MUSE: Microcomputer Users in Secondary 

Education, July 19BT. 



Table 7. Recent surveys of computers in 
schools, 
themselves are *he object of interest ^ 

■ Computer-assisted learning, in which 
computers are used to teach other 
subjects. 

■ Administration where a computer is used 
in helping to run the school. 
Computer-assisted learning includes ail 

aspects of computer use in which the machine 
plays a direct part in teaching the student. 
Computers can help teachers by taking over 
the dull, routine, repetitive tasks — like 
marking, calculating class orders, working out 
attendance records and scheduling pupils to 
resources — in fact* acting as a clerical 
assistant. 

The most remarkable commercial system of 
this kind is Plato, which has come to Britain 
from the U.S. Users of Plato terminals can log 
in what they want with their own code. The 
computer guides them through their chosen 
course s 3 managing [he statistics of their 
progress, enabling assessment, supervising the 
use of books, audio-visual and laboratory 
work, and providing interactive learning 
programs r 

Within a decade, small straightforward 
micro-based systems of this versatility will be 
able to handle courses held on EFROMs or 
bubble memories;. FUlo is essentially a 
development of the programmcd-learning 
technology of the 1960s, and there is still very 
little that is useful. Material available from a 
typical single frame is shown in figure 1. 

Individual teachers are spending a lor of 
time trying to mirror their own teaching 
technique — one of flexibility, sophistication, 
and explanation — to two computer programs. 
An incorrect answer should lead to real help; a 
correct input should be checked for under- 
standing. 

Programming for teaching calls for a 
combination of teaching expertise and 
programming ability — and a great dual of 
lime. Rush leads to rubbish, and there's plenty 
of rubbish around. One of the reasons for the 



failure of many mechanical teaching aids in 
the 1970s was the general inadequacy of the 
software. 

To many people, computer-assisted learning 
is viewed as just one of the many resources 
available for a class It is viewed in 
conjunction with the chalk board, a projector, 
maps and hand-outs, and specialist laboratory 
equipment. Its applications include: 
■computation in geography, mathematics 

and the sciences; 
■development, testing and using models in 

the practical and social sciences, and in 

sports; 
■retrieval of stored data; 
■graphical presentation of data; 
■educational game-playing and assimila- 
tions in social, general and science 

subjects; 
■reinforcement and testing; 
■control of laboratory experiments and data 

capture, 

Software problems and teachers' inex- 
perience remain major bugbears. Though 
most schools with a micro probably have a 
couple of real enthusiasts on the staff, ihe 




Figure 2. Number of entries for computer- 
studies papers in pubiic examinations. 

majority of serving teachers have no know- 
ledge of computing and its potential Those 
teachers who are expert in compuiing still 
have a full teaching timetable of their own, 
and no time for good software development, 
Ideas often have to come from the pupils 
themselves 

Though computer- assisted learning has not 
travelled far towards achieving its potential, it 
is probably the most important area of 
educational computing. Another important 
field at Ehe moment is computer studies. 
There cannot be many people who would 
deny that schools should ai tempt to teach 
something of our new micro- wo rid. 

(continued on next page} 



YOUR COMPUTER, DECEMBER Ittl 45 



fcontinuvd from previous p&ge) 

Thai attempt is being made in several ways. 
Firstly j there are signs of change in this 
direction in formal examination syllabuses, 

particularly in physics, maths and lechnology, 
where some knowledge of simple micro 
electronics and computer arithmetic is coming 
10 be expected. 

A number of examination boards now offer 
papers in computer studies — see figure 2. 
Opinions of the value of these examinations 
vary greatly fc but even if they give I title direct 
career benefit 10 the students* they do fulfil the 
essential task of helping teachers learn basic 
principles- The same applies to test editing in 
commerce departments, a related growing 
field. 

Computer-awareness courses are potentially 
the most useful^ giving a brief introduction to 
computers and Their uses for all pupils. They 
are usually short courses, often run fairly 
informally as pan of general or social studies. 

Their aim is to indicate in broad outline 
what computers are, what they do, and their 
possible effects on society. Topics which 
ought to be covered include (he Eulure 
electronic office, employment effects, privacy 
and high-grade robots, for instance. 

The fundamentals of computer pro- 
gramming may also be covered in these 
classes. Not all children need to learn pro- 
gramming* but most can benefit from the 
logical approach and some are itching 10 make 
their own arcade games. 

Attendance ai an introductory course should 
be a requirement of all pupils wanting to get 
into the computer club. The numbers 
involved in club activities and the high 
demand on non-lesson lime mean chat [he club 
should be self-supervised as much as possible. 
The teacher ought to be available to give 
advice, but need not act as a detailed organiser. 

In many schools *, the computer club is a 
haven for hardware freaks and so ft wu re 
addicts. It should also provide a unique oppor- 
tunity for academically less able pupils to 
develop new and enjoyable skills. This kind of 
work can lead to the development of little 
business enterprises", again providing a great 
deal of real education. 

Figure 3, The exercise boat: of the fufure? A 

smtifl A4-sized computer could tr&ve 
tfemGftdouS potential in school end &f home. 



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Practice! microprocessor work wtft the fVanocomputer, 



School administration by computer is begin- 
ning to take off. The direct beneficiaries- arc 
[he staff who are relieved of much of their 
routine work. 

There are now programs which make a fair 
attempt at timetabling — the deputv head's 
nightmare. Computer assistance in the library, 
resource cent re , and general olice can much 
improve working conditions. Some folk arc 
even using Sinclair's to handle the tuck-shop 
accounts. 

Data capture and process control are areas 
with enormous potential which are, as ycU 
hardly touched, Science laboratories and 
technology workshops are the sites for these 
developments in the first instance, but 
doubtless other areas will get the spin-off later. 
Computerised thermostats and the old 
favourite j. model traffic- light control, are 
appearing at more and more school open days, 
Pressure from pupils will accelerate the 
process, 

The pessimistic view for the future — one 
fairly often expressed — is that schools' 
computers will follow the 1960s' teaching 
machines into oblivion, leaving hardly a ripple 
behind. Of ^course, teaching is a pretty 
conservative profession which remains highly 
labour-intensive despite alt the exisiinii 
technological claims. Sceptics compare 
schools' computing to the audio-visual 
vogue of a decade ago. Certainly > a lot of 
money was wasted at thai time, but now 
equilibrium has been reached at a much higher 
level of use than before. 

At the other end of the spectrum arc the 
visionaries who see schools reduced to social 
development or "play" centres. Learning 
would, they say, take place at home or in small 
units under the management of computers 
with little human intervention. 

Who knows? Maybe thai will come in a 
number of decades. Certainly there are some 
children Vd be glad to hand over to such a 



system, and many who would do well on it. 

Between these extremes he ihe more realistic 
possibilities. They will follow from progress 
towards large metmry on cheap chips input 
pads, flat- screen output, plus-in EPROM 
language* programs and data 

Within five or 3 year* we could have a flat 
A4**ixed niulii-purpuve computet which 

would be capable of everything j 64 K micro 
could do and more, and could communicate 
with the local databases and other machines, 
If the cost came down to around £30 at today's 
prices,, it would have tremendous potential in 
schools as well as in the home — see figure 3, 

Before that day dawns, we should all have 
developed a fair idea of how |0 use such a 
machine in The classroom. So Jet's get on with 
it. 

Several national educational computing 
associations already exist. The largest and 
most active is MUSE — Microcomputer- 
Users in Secondary Education — whose 
membership gains access to a network of user, 
regional and local groups with many activities, 
The three-day annual meeting takes place in 
July, Details a re jivjiiliihk irom Hob Trigger* 
MUSE, J-recpost, Bromsgrove, B6| OJT for 
details. 

There are far too many books on educational 
computing to give a comprehensive list here. 
One recent addition to the list is Mmdswrtm 
by Professor Seymour Paper t, which could 
become very influential. It is published by 
Harvester Press at 0,95, Run, tempt* fer t run 
by Anthony Qettinger, published by 
Mac mi 11 an, may not be in print any longer — 
it firs i appeared in 1%9 — but I still find a 
scan of it most safutory when my enthusiasm 
runs oue of bounds. 

Computing is exciting to many of our pupil*, 
including the less able, h is richly rewarding 
to find a trouble-maker suddenly immersed in 
a program and thereby gain an interest in 
school work. Believe me, it does happen. ■ 



46 YOUR COMPUTER, DECEMBER 1981 



ZX8I 

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YOUR COMPUTER, DECEMBER iSai 47 



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COMPUTACALC ZX 

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48 YOUR COMPUTER, DECEMBER 1381 





PERSONAL 
COMPUTER 



Sinclair ZX81 Personal Com 
the heart of a system 
that grows with you. 



1980 saw a genuine breakthrough - 
the Sinclair ZX80, world's first com- 
plete personal computer for under 
£100, Not surprisingly, over 50000 
were sold. 

In March 1981, the Sinclair lead 
increased dramatically. For just 
£69.95 the Sinclair ZX81 offers even 
more advanced facilities at an even 
lower price Initially, even we were 
surprised by the demand - over 
50,000 in the first 3 months! 

Today, the Sinclair ZX81 is the 
heart of a computer system, You can 
add 16-times more memory with the 
ZX RAM pack TheZX Printer offers 
an unbeatable combination of 
performance and price. And the ZX 
Software library is growing every day. 

Lower price: higher capability 

With the 2X81, its still very simple to 
teach yourself computing, but the 
ZX81 packs even greater working 
capability than the ZXS0. 

[t uses the same microprocessor, 
but incorporates a new, more power- 
ful 8K BASIC ROM - the trained 
intelligence 1 of the computer. This 
chip works in decimals, handles logs 
and trig, allows you to plot graphs, 
and builds up animated displays. 

And theZXSl incorporates other 
operation refinements - the facility 
to load and save named programs 
on cassette, for exam pie, and to 
drive the new ZX Printer 





Eve-ryZXGt come £ wilh a Cflmprehensi-ve . spfloally- written 
manual - 4 com^eta couwm BASIC programming, from 
firsl principles la cofnptox programs 



Higher specification lower price — 
how's it done? 

Quite simply, by design. The ZX8Q 
reduced the chips in a working 
computer from 40 or so, to 21 The 
ZX81 reduces the 21 to 4! 

The secret lies in a totally new 
master chip. Designed by Sinclair 
and custom-built in Britain, this 
unique chip replaces 18 chips from 
theZXSO! 

New, improved specification 

• Z80A micro-processor - new 
faster version of the famous Z80 
chip, widely recognised as the best 
ever made. 

• Unique 'one-touch* key word 
entry: the ZXS1 eliminates a great 
deal of tiresome typing. Key words 
(RUN, LIST, PRINT, etc.) have their 
own single -key entry. 

• Unique syntax-check and report 
codes identify programming errors 
immediately. 

• Full range of mathematical and 
scientific functions accurate to eight 
decimal places. 

• Graph-drawing and animated- 
display facilities. 

• Multi-dimensional string and 
numerical arrays. 

• Up to 26 FOR/NEXT loops. 

• Randomise function - useful for 
games as well as serious applications. 

• Cassette LOAD and SAVE wfth 
named programs. 

• lK-by!e RAM expandable to 16K 
bytes with Sinclair RAM pack 

• Able to drive the new Sinclair 
printer. 

• Advanced 4-chip design; micro- 
processor, ROM, RAM, plus master 
chip - unique, custonvbuift chip 
replacing 18 ZX80 chips, 




Built: 




Kit or built - it's up to you! 
You'll be surprised how easy the 
ZX81 kit is to build: just four chips to 
assemble (plus, of course the other 
discrete components) -a few hours 1 
work with a fine-tipped soldering iron. 
And you may already have a suitable 
mains adaptor - 600 mA at 9 VDC 
nominal unregulated (supplied with 
built version). 

Kit and built versions come com' 
plete with all leads to connect to 
your TV {colour or black and white) 
and cassette recorder. 





I6K- byte RAM 
pack for massive 
add-on memory. 



Designed as a complete module to 
fit yourSinclairZXSO or ZX81. the 
RAM pack sinn ply plugs into the 
existing expansion port at the rear 
of t he computer to multiply your 
data/program storage by 16! 

Use it for long and complex 
programs or as a personal database. 
Yet it costs as I ittfe as half t he price 
of competitive additional memory. 

With the RAM pack, you can 
also run some of the more sophisti- 
cated ZX Software - the Business & 
Household management systems 
for example- 




ZX8I 



Available now- 
the ZX Printer 
for only £49.^ 

Designed exclusively for use with 
the ZX81 {and ZX80 with 8K BASI C 
ROM), the printer offers full alpha- 
numerics and highly sophisticated 
graphics. 

A special feature is COPY, which 
prints out exactly what is on the 
whole TV screen without the need 
for further int ructions. 



At last you can have a hard copy 
of your program listings -particularly 
useful when writing or editing 
programs, 

And of cou rse you can print out 
your results for permanent records 
or sending to a friend. 

Printing speed is 50 characters 
per second, with 32 characters per 
line and 9 lines per vertical inch. 

TheZXPrinterconnectstotherear 
of your computer - using a stackable 
connector so you can plug in a RAM 
pack as well. A roll of paper (65 ft 
long x 4 in wide) is supplied, along 
with full instructions. 



How to order your ZX81 by cheque, postal order, Access. 

BY PHONE - Access, Barclaycard or Barclaycard orTrustcard 



Trustcard holders can call 
01-200 0200 for personal attention 
24 hours a day, every day, 
BY FREEPOST - use the no-stamp- 
needed coupon below. You can pay 



EITHER WAY - please allow up to 
28 days for delivery. And there's a 
14-day money-back option. We want 
you to be satisfied beyond doubt - 
and we have no doubt that you win be. 



To: Sinclair Raaearch Ltd. FREEPQST 7. Cambridge, CB2 IVY, 



Order 



6 Kings Parade, Cambridge. Cambs., CB2 1SN 
Tek(0S76) 86104 & 21282. 



Qt* 


(tarn 


Cod* 


Item price 
£ 


Total 
£ 




Sinclair ZX&1 Person a J Computer kit(s}. Price includes 
ZXB1 BASIC manual, excludes mams adaptor. 


12 


49+W 






Ready-assembled SincLairZXSi Personal Computer(s) 
Price includes ZX&i BASIC manual and mains adaptor. 


11 


69.95 






Mains Adapiortsj (600mA at 9 V DC nominal unregulated). 


TO 


e.95 






16K-BVTE RAM pack 


18 


4A93 






Sinclair ZX Printer. 


27 


mm 






8KBA5iCflOMtotitZX80 


17 


19.95 






p ri stand Packing, 






2.96 



I 



□ Please tick if you requires VAT receipt TOTAL £ - 

*l en close a c haque/ pos ta I o rder payable to Sin clair R e sea reh Ltd , for £ — 

*Please charge to my Access/Bafclaycard/Trustcard account no. 

*Pic a*e diHete'c&mpitt e as apphublr I I - I I I LI 1 I i [ i 1 | I | 

Pteastprmi 

Name: Mr/Mrs/Miss 1111111111111111111! I 

Address:! I 1 I I I M I I I I 1 I ! I 1 1 I I II I 1 

I 1 I 1 I I I I 1 I I II I II I I I I 1 I I I I I I I 
FREEPOST -no stamp needed. »*« | 






A : the ZX8I compares with other personal computers 



SYSTEM IDENTIFICATION 



ROM 



ZX81 



BK 



zxso 



4K 



ACORN 
ATOM 

8K 



APPLE II 
PLUS 

8K 



PET 
2001 

14K 



TRSSO 

LEVEL \ 

4K - 



THS80 
LEVEL II 

12K 



G Ul DE P RICE Basic unit - i nt VAT 

Unit plus tfiK RAM (*I2K RAM) 



£70 
£120 



£100 
£150 



£175 

£.2 BO* 



£630 
£630 



£435 
£530 



£290 
£360 



£375 
£375 



COMMANDS 


LIST, LOAD, NEW, RUN. SAVE 


• 


• 


• 


• 


m 


• 


• 




STATEMENTS 


PRINT, INPUT, LET, GOTO, 
GOSUB/RETURN. FOR/NEXT IF/THEN 




• 


• 


• 


• 




• 






STEP 






* 


• 


• 




• 






TAB 








# 


• 




* 




ARITHMETIC 


ABS.RNO 




m 


• 


m 


• 




# 




FUNCTIONS 


INT 








m 


• 




# 






ATN. COS, EXP, LOG. SGN, SIN, SQR, TAN 








m 


• 




• 






ARCSIN, ARCOS 


















STRING 


CHRS 




* 




m 


« 




• 




FUNCTIONS 


LEN 






• 


m 


• 




# 






ASC(CODE). STRS. VAL. INKE VS 










• 




• 




NUMBERS 


FLOATING PT ±10" 








m 


• 


• 


• 





INTEGERS 



NUMERIC 
VARIABLES 



A-Z 



AA^ZQ 



AivZan-an y a I ph a numeric airing 



STRING *i iB! L 

VARIABLES AStQZS 

A nS to ZnSn~ any alphanumeric character 



NUMERIC SINGLE DIMENSIONAL 

ARRAYS M U LTI DIME NS! O N AL 



DISPLAY 



ROWS 



24 



24 



16 



24 



25 



16 



16 



COLUMNS 

LOW RES GRAPHICS K7 QQ pixels} 



32 



32 



32 



40 



40 



$4 



64 



_H1 RES GRAPHICS (> 40000 pi wis) 



SPECIAL 
FEATURES 



USR [CALL, LINK) 



PEEK, POKE (OR EQUIV) 



Sinclair software 
on cassette* 




The ultimate course 
in ZX8I BASIC 
programming* 



Iff you own a 
Sinclair ZX80 



• »• 



The unprecedented popularity of the 
ZX Series of Sinclair Personal 
Computers has generated a large 
volume of programs written by users. 

Sinclair has undertaken to 
pubfish the most elegant of these on 
pre -recorded cassettes. Each pro- 
gram is carefully vetted for interest 
and quality, and then grouped with 
others to form single-subject 
cassettes. 

Software currently available 
includes games, junior education, 
and business/household manage- 
ment systems. You'll receive a 
Sinclair ZX Software catalogue with 
your ZX81 - or see our separate 
advertisement in this magazine. 





Some peopte prefer to learn their 
programming from books For them, 
theZX81 BASIC manual is ideal. 

But many have expressed a 
preference to learn on the machine, 
through the machine. Hence the 
new cassette-based ZX81 Learning 
Lab. 

The package comprises a 160- 
page manual and 8 cassettes, 20 
programs, each demonstrating a 
particular aspect of ZX81 program* 
ming r are spread over 6 of the 
cassettes. The other two are blank 
practice cassettes. 

Full details with your SinclairZXSt 



The new 8K BASIC ROM used in the 
Sinclair ZX81 is available to ZX80 
owners as a drop-in replacement 
chip. (Complete with new keyboard 
template and operating manual.) 

With the exception of animated 
graphics, all the advanced features 
of the ZX81 are now available on 
yourZXSO - including the ability to 
drive the Sinclair ZX Printer, 




6 Kings Parade, Cambridge, Camb£>, CB21SN, 
Tel: (0276) 66104 & 21 282. 



VIC-20 CASSETTES 



BY 

NICK HAMPSHIRE 



1 


2 

1 1 


3 
i — i 


4 

1 — 1 


5 

1 1 


6 
■ — i 


I 1 


izzr 


-C3- 






•^r 



A 


B C D E F 


Pin# 


FUNCTION 


A-1 


GND 


B2 


+5V 


C-3 


Cassette motor 


D-4 


Cassette read 


E-5 


Cassette write 


P6 


Cassette switch 



Figure 2 VtA sssignmentSr 



Vu#l 




V..IP? 


NMI 




na 


CA1 




Cai 


PAO 




RAO 


*W1 




f%i 


PA2 




M2 


p*a 




PA 3 


FA4 




FA* 


PA* 




PAS 


we- 


— Cfttttit* iwrich 


RA8 


w 




PA7 


C47- 


— CHHttt molar 


CA2 


Cb* 




CB1 


PBO 




PW 


FBI 




Pffl 


pe* 




PW 


FrbJ 




P03- 


FRJ 




mt 


pes 




PBS 


poa 




PB6 


w 




PQ7 


CB2 




CB2 


SfrllO 




S91?0 




S*13F 



-Ci»!wtlrre«j 



Cassette wfrte 



Hardware 

The '. k HAS a single, external cassette unit 
which is used for program and data storage. 
This unit is connected to the Vk by six lines 
— write, read, motor, sense and two power 
lints, ground and + 5V. The connections are 
shown in figure 1, 

T fhe cassette is controlled by VO lines from 
the two VIA (versatile interface adaptor) chips, 
and you can sec the source of each of the 
cassette- control lines from the VI As in figure 
2. 

The cassette- motor power supply J^« arc 
connected to the interface chips via a three- 
transistor driver which is used to boost the 
power and voltage — it allows the motor to be 
driven dirt: city. The output to The motor is an 
unregulated + 9Y jt a powe: rating of up in 
6DUrnA. The cassette- deck motor can be 
Earned on and off by tolling the CA2 line on 
6522 * I, 

POKE 37148, PEEK (37148? AND 241 OR 14 
tuin$ the motor om 

POKE 37148, PEEK 1 37 148! OR 12 AND NOT 2 
turns it off. 

The sense-line input, line PAfcon VIA* 1, ii 
connected to a switch on ihc easscuc deck 
which senses when either the play, rewind or 



fast forward buttons have been pressed. The 
switch is only required to sense whether or not 
you have pushed the play button during £ 
read- or wriie-to-iape routine. This is done by 
a subroutine at 5F8AB. 

If either the rewind or fast -forward button is 
pressed accident ally in Head of the play button, 
the system, will be unable to Tell the difference 
and will act as if [he play button had been 
preyed. Because recording will start as soon as 
the play button has closed the sense switch, 
you must press the record button first in any 
record routine. 

The cassette read line is connected to the CA I 
line of VIA #2 and the cassette write line to 
line PB3 of VIA # 2. [luring a read operation, 
the operating system uses the setting of the 
CAI interrupt flag in del eei transitions on the 
cassette- read line. The read and write lines are 
controlled entirely by the operating system — 
the only hardware required is signal- amplifica- 
tion and pulse-shoring circuitry. 

These circuits are contained on t smalL 
pnmcd*circuit board within the eassene deck 
Their function is to give correct voltage and 
current to the record head and to amplify the 
input from the read head Thai gives a 5V 
square-wave output capable of producing an 
interrupt on the t;.\: or CAU hnc^. 



figure 3. C&ssette int&rfacv ctfeuft- 



+9W *sv 




Cassette operation techniques 



I\>K NORMAL purposes the cassette deck is 
assigned the device number 1. The I/O 
number of the device currently in use is stored 
in location 186. This number, the logical file 
number, and the secondary address are used 
when saving or retrieving data files from the 
cassette deck. 

The logical Tilt number can be any number 
from I to 255 and is used to allow multiple 
files to be kept on the same device. It is of lit lie 
use with cassette tape and is i mended 
primarily for floppy-disc units. Usually the 
logical file number is the same as the device 
number and is stored in location 164. 

Since it determines the operational mode of 
the cassette, the secondary address is 
important and the current one is stored in 
location 185. The normal default value is zero. 
If the secondary address is zeroj the tape is 
Opened for a read operation. If it is set to one, 
it is opened for a write operation and if two, it 



is opened for a write, and an end-of«tape 
header is forced when the file is closed. 

The Vic operating system is configured to 
allow two types of Tile to be stored on cassette; 
program files and data files, These names are 
however rather misleading since a program 
can be stored as a data file and data can be 
stored as a program [lie. 

The difference between the two types is not 
in iheir application bnt ia the way the contents 
of the machine's memory' is recorded. Instead 
of program and data files, we must look on 
i hem as binary and ASCII files. 

A binary file is usually used to store 
programs* since it is created by the operating 
system to store the contents of memory 
between a starting location and an end 
location. It is called a binary file because it 
stores on tape the binary value in each 
memory location within the assigned memory 
area. 



Basic statements are stored in memory using 
tokens. The use of tokens means that Ha sic 
commands arc not stored in the same manner 
as they are listed on the display or were 
entered from the keyboard. Instead, they are 
stored in memory in a partly-encoded form. 
Being partly encoded, a binary file is a quicker 
and more effieiem way of storing programs. 
Binary files are essential when saving and 
loading machine-code programs. 

The starting address from which a binary 
file will be saved is stored in locations 172 and 
171- These location* arc loaded by ihe save 
routine, with the memory locations at which 
the save will begin normally set to and 4, 
thereby pointing to the start of the Basic text 
area at 1024, 

They can be altered by the save routine 10 
point to any Location in memory. The end 
address of the area of memory 10 be saved is 

stored in local ions 174 and 175, Normally, 
when saving a Basic program, these are set to 
the address of the double-zero byte which 



YOUR COMPUTER, DECEMBER 198! 53 



(continued from prevtous page) 

terminates the Link address. The end address 

can be altered to any desired location, 

To change either of chtst: addresses one 
cannot use the normal save routine since it 
automatically initialises these locations. 
Instead, one must write a small machine-cade 
initialisation rouliue incorporating the desired 
operating-system subroutines, By default, a 
Save command will write a binary tile and a 
Load command will read a binary file. 

ASCII files are normally used to store data 
but they can be used to store programs. Their 
format is the same as that displayed on the 
screen or entered from the keyboard, ASCII 
files are created or read almost exclusively by 
instructions from within a Basic program, A 
binary tile is created or read mostly by direct 
instructions, though the Load and Save 
instructions can be used within a program. 

An ASCII llie must first be opened with an 
Open statement which s pec: i ties the logical 
file, device number, secondary address and file 
name. The operating system interprets these 
parameters and allows the user to read or write 
the hie KJ the specified device. 

bail is written to an ASCII file on a 
particular device with a command to Print to 
the specified logical file number, and data is 
read by a Read from the logical*- file command. 

Tape buffer 

Whereas a binary file is loaded with the 
contents of successive memory locations, an 
ASCII file is loaded with a string of variables. 
Storing these would require the tape TO be 
turned on and off repeatedly, retaining a few 
bytes of data at a time. The Vic overcomes this 
by having a 192- byte tape buffer into which all 
data to be written to, or read from tape is 
loaded. Only when this buffer is full is the tape 
motor turned on. 

Data is stored on tape in blocks of 192 bytes 
and since the motor is turned on and off 
between blocks, a two* second interval is left 
between blocks to allow the motor to 
accelerate and decelerate. The beginning of 
:hc 192-eharacter buffer starts at address 828; 
the pointer to the start of the buffer is located 
at addresses 178 and 179; the number of 
s I m racier s in a buffer is stored at location 166. 

These locations can be used by the pro- 
grammer to control the amount of space left in 
a data file. If, having opened a file on ljsscUc* 
the command Poke 166,19 1 is executed, then 
the contents of the tape buffer — even if empty 
— are loaded w\ ro the tape. If reemds lik- kc\n 
in multiples of 191 bytes, we can very easily 
keep null or partially-filled records allowing 
future data expansion. 

Whether the file being stored is binary or 
ASCII, the recording method used is the same 
and involves an encoding method peculiar to 
Commodore and designed to ensure maximum 
reliability of recording and playback. Each 
byte of data or program is encoded by the 
operating system using pates of three distinct 
audio frequencies, these are: long pulses with a 
frequency of 1,488Hz, medium pulses at 
1,953Hz and short pulses at 2 s S40Hz, 

All these pulses are square waves with a 
mark-space ratio of 1:1, One cycle of a 
medium frequency is 256^s. in the high state 
and 2 s 56^s. in the low state, 

The operating system takes about 9ms. to 



record a byte of data consisting of the eighi 

data bits, a word-marker hit and yn odd-parity 
bit, The data bits are either ones or zeros and 
are encoded by a sequence of medium and 
short pulses, A one is one cycle of a medium- 
length pulse followed by one cycle of a short- 
length pulse and zero is one cycle of a short- 
length pulse followed by one cycle of a 
medium-length pulse. Each bit consists of two 
square- wave pulse cycles, one short and one 
medium with a total duration of 864jis_ The 
wave- form timing is shown in the diagram in 
figure 4. 

The odd- parity bit is required for error 
checking and is encoded like the eighi data bits 
— using a long and short pulse. Its slate is 
determined by the com en is of the eight data 
bits. The word marker separates each byte of 
data and also signals to the operating system 
the beginning of each byte. The word marker 
is encoded as one cycle of a long pulse 
followed by one cycle of a medium pulse, see 
figure 4. 



ft** MQutwt tor tag* " ' " ferf 



H6- 



17** 



r 



Pl*t bacuBrte K* logic. & bfl 



J 



•**» 



r 



396*1* 



J 



Jft« 



r 



FigurQ 4. Operating system put$$ sequence. 



Since a byte of data is recorded in just 
3,96ms-, is 192-byte block of data in an ASCII 
file should be recorded in slightly more than 1 .7 
seconds. However, timing such a recording 
shows that it takes 5-7 second*. There arc 
two causes for this discrepancy in timing. 
First s to reduce the possibility of audio 
dropout s j the data is recorded twice. Secondly, 
a two-second inter* record gap is left between 
each record of 192 byteSn 

The extensive use of error-checking tech- 
niques is one reason why the tape system on ihe 
Vic is so much better than that available on 
most other popular computers. There are two 
levels of error checking. The first divides the 
data into blocks of eight bytes and then 
computes a ninth byte, the check-sum digit, 
The check-sum is obtained by adding the eight 
data bytes together; it is the least -significant 
byte of the result. 

On reading the tape, if one bit in the eight 
bytes is dropped and a zero becomes a one or 
vice versa, the checksum can be used to detect 
this error. To do this, the same procedure to 
calculate the check digit is performed. The 
result will be different to that stored in byte 9 
which is the check digk of that block 
computed when the tape was recorded, 

The second level of error checking involves 
recording each block of data twice, This allows 
errors detected by the check digit to be 
corrected during the second reading of the 
192-bytc data block, By recording the data 
twice j a verification can be performed by 
comparing the contents of the two blocks. 



This will detect the few errors not detected by 
the check-sum. 

The use of pulse sequences, rather than two 
frequencies as in a standard FSK (frequency- 
shift keying) recur ding, has a greal ad van I age 
since it allows the operating system to 
compensate easily for variations in recording 
speed. Normally, a hardware phase-loeked- 
loop circuit weiuld be used to lock the system 
on to the correct frequencies transmitted from 
the tape head. The Vic, however, uses soft- 
ware to perform this process. 

Inter-record gaps 

A IG-second leader is written on the tape 
be tare recording of the data or program 
commences. This leader has two functions: 
first* it allows the tape motor to reach rhe 
correct speed, and secondly, the sequence of 
short pulses written on the leader is used to 
synchronise the read-routine timing to the 
Timing on the tape. 

The operating system can thus produce a 
correction factor which allows a very uide 
variation in tape speed without affecting 
reading. The system timing used to perform 
both reading and writing is very accurate, 
based as it is on the crystal-Cont rolled system 
clock and timer 1 j.nd i:rner 2 of VIA * 2. 
Inter-record gaps are only used in ASCII files 
and their function is to allow the tape motor 
time to decelerate after being turned oJT and 
accelerate to the correct speed when turned on 
prior to a block read or write. 

Kach inter- record gap is approximately two 
seconds loop and is rtvorded as a sequence of 
short pulses in the smne manner as the 
10-second leader. There is also a pp between 
blocks. VThcft the first block of 192 bytes is 
recorded, it is followed by a block end-marker 
which consists of one single, long pulse 
followed by more than 50 cycles of short 
pulses. Then the second recording of the 192 
block starts. 

The first record written on the tape after the 
lOsccond leader in boih ASCII and binary 
files is a 193 -character ille-header block. The 
file header contains the name of the file* the 
starting memory location* and the end loca* 
tion, In an ASCII file these addresses are the 
beginning and end of the tape buffer; in a 
binary file they point to the area of memory in 
which the program is to be stored. 

The file name can be up to 128 bytes long, 
ihe length of the file name is stored in location 
183* and when read is compared with the 
requested file name in the Load or Open 
command. If the name is the same, the operat- 
ing system will read the file; if diflferem, it will 
search for the nest 10-sccond intcr-filegap and 
another header block, 

The file name is stored during a read or 
write operation in a block memory whose 
starting address is stored in locations 137 and 
138, When the operation is completed these 
are reset to point to a location in the operating 
system. The starting location is normally set lo 
the beginning of the user-memory area. 

The starting address is pointed to by the 
contents of locations 172 and J 73. The end 
address is stored in locations 174 and 175. 
Normally this is the highest byte of memory 
occupied by the program; it can, however, be 
altered to point lo any address, providing it is 
II greater than the start address. H 



54 YOUR COMPUTER, DECEMBER 1961 



NEW ATOM SOFTWARE 

SOFTSCREEN OK RAM) only£11.40incl. 

For the firs! lime ATOM owners can have facilities of ihe B-B-C- 
Micro on their computer, e.g. mixed text and high resolution 
graphics, definable text window areas. Also for the first \\m$ m or\ 
an Atom, 40 characters per line. Other features include: 
•Extensive cursor contours 

• T&Xt iii all modes 

•Upper, lower case and inverse tfift 
•40 k 24 text 

• Defmgble text area, etc. etc. 

INVADERS 1 12K RAM) only £7.50 incl. 

A new version and wilhout doubt tetter than all those reviewed 
la si month. More features, including six skill levels and high 
scores, 'walking" invaders, sound effects, free from video ng»se 
High resolution graphics and a high speed game. Ask for more 

dmflt. 

ALARM CLOCK AND SOUND EFFECTS 

(2K RAM each) only £4. 95 for the two 

Incredfble value. The clock keeps accurate time white other 
programs are running. Sound effects give a range of tone and 
noise effects without stopping the Atom Both programs need 
6522 VIA. Ask for more detail 

WANTED: Good quality software for the BBC Micro end Acorn 
Atom. 20% royalties paid. Further details on request. 

MAIL ORDER ONLY 




OMPUTER 
□NCERTS 



16WAV&IDE 
CHIPPEHHELD 
HERTS. WD4 9JJ 
Tmk I09J77> 6SSS 



*BIG EARS* 



SPEECH 

INPUT 

FOR 

YOUR 

COMPUTER! 



SPOICH «OOGWrntW 



— .,"- t fV*Q I 



B]G EARS opens the door to direct 
man-machine communication. The system 
comprises analogue frequency separation fitters, 
preamps and signat conversion, together with a quality 
microphone and extensive software. 
Words, in any language, are stored as , ■vo^ce■prlnts ,, by 
simply repeating them a few times in 'learn" mode. 
Using keyword selection techniques, large vocabularies 
can be constructed. 

Use BIG EARS as a front end for any application: data 
enquiry, robot control, starwars — the possibilities are 
unlimited.. D /I Q I 
BUILT, TESTED & GUARANTEED ONLY t*4 */ ! 
PRICE INCLUDES POSTAGE * PACKING PLEASE ADD VAT AT 15% 
PLEASE STATE COMPUTER: UK101. SUPERBOARD, NA5COM2. 
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I 33/35 Portugal Road, Woking, Surrey CU21 5JE 



VOUR COMPUTER, DECEMBER tW 66 



ACORN ATOM MACHINE 



I DECIDED to adopt the very simple approach 

of using a talcuhicd Gosub — lint GO — 10 

pick the appropriate print line. Each 

individual digit is printed separately after the 

address to avoid suppressing zeros. To help 

you understand the piogram, here are some I the Atom's advanced features. For example, 

notes: ? - PEEK or POKE r P. - PRINT, % = Remainder 

Una m: Sets P, Q and R to the ne*i Three bytes After division, a 5 b, c, etc, are labels for Goto 

of cod* then prints the address focation and or Gosub, P.&L means Print the variable L in 

the first byte at ihat toeaiwn in hexadecimal. hestldecimal form, @ is used as The field size 

Line 45: Calculate* tf* individual hex digits for ^ t j R m _ ins R Li 

of the n^xt two byres for later printing. A£ . i „ . 

UM 50: T is •« to the uc«td he* dig,t of the """fw 89 * interesting a, n : uy» Bool^n 

instruction code already printed out .mine 40. dl S ebra I0 P™ * calculate! forward or 

Line 55: If the second digit of the instruction backward branch destination as appropriate. 

is 3, 7. B or F, it is not an instruction code and Having entered and checked the program, 

this section of machine code is either gaibaye what does one do ulih it? Wi- need some 

or data. This line picks ihem out H we figure 1 . machine code io disassemble; the obvious first 

Line 60: Jump calculation and Gosub. ^icc is the residem operating svstem, 

Lines 75 to 77: Subroutines to print the appro- 1 5tarled bv exp | oring Thc variouS j umps and 

pnate numtoer of bytes after ihe MMrucnon Subr0ll[ines associated wi|h tnput and output 

code. This is erlh&r none, one or two. A t , . 1 r Z .^ 

Lines 78 to 83: Subuuiira to pffM the dsscnp- artd ^covered the section of code responsible 

ikinlolio^^ the assembly mnemonic. tar rolling ihe screen, This routine is 

Lines 100+ : Initial jump locations where each normally used only when a Prim statement 

line number >$ equal IO 100 4 the value of the would otherwise move o(T the bottom of the 

instruction cade. screen. 

All ihe numbers are primed in hexadecimal All it docs is copy each character into the 

form for compactness, allowing each complete line above and then blank out the bottom line, 

instruction group to be printed Oil one line. This shon piece of code is very useful. 

It should be possible to convert this program especially with the Atom's ability to Link and 

to run on any machine which uses a 6502 execute machine code ht any address. Add to 

processor assuming that you can understand 1 this the orher facility provided on the Atom 

Figure 7. Atom op-cod&s, sftvwing rtufnber of bytes. 



Roy Burgin noticed several advertisements for machine-code 

disassemblers for the Acorn Atom, They set him thinking that a 

disassembler would be a useful tool, so one evening he sat down 

at the keyboard and set about writing one for himself, 

whereby Basic variables A, X and Y arc 
automatically transferred into the 







O 


1 


2 


3 


4 


5 


6 


7 


8 


9 


A 


B ' 


c 


D 


E 


F 







BRK 

1 


ORA 








ORA 

Z 
2 


ASL 
Z 2 




"PHP 1 
1 


ORA 
IM 
2 


AsLA 

1 






OH A 
ABS 
2 


ASL 

ABS 
? 






1 


BPL 


ORA 

(ll.V 

2 








ORA 

7 X 

2 


ASL 




CLC 

f 


ORA 
Ap¥ 

3 








ORA 
AX 
3 


ASL 
A r X 
3 






2 


JSfl 

3 


AND 

(i + xi 2 






BIT 


AND 
2 


Ml 




PLP 

-I 


AMD 
IM 

2 


ROLA 

1 




ABS 

3 


AND 
ABS 
3 


ROL 






3 


BMI 

2 


AND 








and! 
z,x 

? 


ROL 
Z.X 
2 




MET 

1 


AND 
AN 
3 








AND 
A.X 
3 


ROL 
A.X 

a 






4 


RTI 

1 


eon 








EOR 


LSR 
Z 7 




PHA 

1 


EOR 

IM 2 


LSRA 
1 




J MP 
ABS 


EOR 


LSR 






5 


BVC 
2 


eor 1 

{|)V 
2 








EOR 
Z.X 

2 


15R 




CLI 
1 


EOR 








EOR 

A.X 
3 


A,K 






6 


ATS 
l 


ADC 
■:.X: 
2 








ADC 

Z 


ROR 




PLA 

1 


ADC 
IM 

2 


ROflA 

l 




MP 

IND 

- 


ADC 

ABS 

? 


ABS 
1 






7 


BVS 
? 


ADC 
<l> r Y 

2 








ADC 
Z.X 


ROR 

z.x^ 




SEI 


aikT 

A.Y 

3 








ADC 
A,X 
3 


ROR 
A^ 3 




+* 


2 


2 


en 
6 


8 




STA 
(l,X) 

2 






STV 

z 

2 


SYa 

z 


SIX 

z 

2 




DEY 

1 




TXA 

1 




STY 

AB5 
4 


STA 

ABS 
1 


STX 

AB8 
3 






9 


BCC 
2 


STA 






STV 


STA 

2,K 3 


STX 




Yva 


4ta 

A,Y 3 


txs 

1 






STA 
A.X a 


3 






A 


LDY 
I 


LDA 
2 


LDX 
IM 
2 




LOT 

Z 
2 


LDA 

Z 
2 


LDX 

Z 
2 




TAV 

1 


IM 
1 


TAX 

• 




LDY 

ABS 

a 


LDA 

ABS 

3 


LDX 
A6S 






B 


0CS 


LDA 
(l),Y 
z 






LDY 
ZJt 
2 


LOA 

Z * 

? 


LDX 

z.v 

2 




C uV 

1 


LDA 
A*, 


TSX 
1 




LDV 

A.X 
J 


LDA 
A.X 

3 


LOX 
A.Y 






C 


CPY 
2 


CMP 






Cpy 

z 

2 


CMP 


DEC 

Z 2 




INY 

1 


CMP 
rM 2 


DEX 
1 




CPY 

ABS 

n 


CMP 
ABS 

J 


DEC 






D 


2 


CMP 

my 
2 








Z.X 

2 


DEC 
ZX 
2 




CLD 


CMP 
A H Y 
3 








CMP 

AX 
3 


DEC 
A,X 3 






E 


2 


sec 

tut 

2 






z 
2 


SBC 

z 

2 


INC 

z 

2 




INX 

■ 


SBC 

IM 

2 


NOP 

1 




cpx 

ABS 

3 


ASS 


INC 
ASS 

a 






F 


BEO 

3 


SBC 








s&c 

Z.X 

2 


INC 

z.* 2 




SED 

1 


SBC 
A.Y 








SBC 

A,X 3 


INC 
AX, 





MNEMONIC OPERATION 
No of BYTES 



accumulator, the X register and the Y register 
u-h^ncver Link l* used, jnd you tan dn magic. 
By placing the right numbers in A und Y, you 
can achieve the following: 

■ Keep up 10 seven i.nes static at ihe top of the 
screen while scrolfing the lower p^r|: $&ti 
demonstration program. The Y register is 
normally loaded wilh 32 before scrolling. 
That is to avoid scrolling ihe top line into 
nothing. IF ihe Basic variable Y is set equal to 
any number greater than this and less thqn 
255. Ehen the exira number of characters will 
be lei l unscroliect when used with Basic code 

LINK* FEOA 
Use in muEtipEes of 32 to scroll whole lines. 

■ Keep seven or more lines SWic whilo 
scrolling the lower pan by omitting the first 
section of code which scfolls the lop of the 
screen and Linking into the sect-ion which 
scrolls the bottom half only - again setting 
the number of unscrolled characters in the 
Basic variable Y. This Time Ths code does not 
wart for t ho frame refresh so i* is advisable to 
include a Wail statement. So this ume the 
code is 

WAtT:LINKp FE19 

■ Blank 32 characters from the cu'sor position. 
This uses the routine which normally blanks 
ihe bottom line of the screen but n uses for 
reference the cursor position which is stored 
in locations # DE and w DF and this means 
that 32 characters will be blanked from 
wherever the cursor happens to be . The code 
is: 

LINK* FE22 

■ Blank up to four fines from the cursor 
position. Again, ihe Basic variable V is used 
to indicate: the number of characters to be 
blanked, fess one, and we Link into the code 
after the poms where the V register would 
normally be loaded. The code is; 

Y- (number of characters - 1 \\ LINK* FE24 

■ Fill up to four lines from the cursor position 
with any chosen character. This *s an 
extension of the last one and is. very fast with 
four tines being filled within the frame refresh 
lime - Basic prints only about eight 
characters m this time. We sei She Basic 
variable Y to the number of characters — 
minus one as before - and the Basic variable 
A to the character code of the chosen 
character. Thus we have: 

Y E (number of characters - 1 ) 
A = Ithe chosen character code value) 
LinM F£26 
To see just how fast this routine is, try 
typing: 
Y-127 

DO A=RND%12B;WA1T;UNK FE2G; U.O 
After pressing Return, [hb totally useless 
piece of code will cause the four lines 
following it to be completely titled with a 
random character and then filled^ over and 
over again, about 30 times per second — so 
111 si [hiii vim L-;miH>[ rc^ftnsst uny of I lie 
characters. 

A more useful method of using this routine 
can be achieved by directing the position of 



56 VOUFT COMPUTER. DECEMBER 13S1 







• I 



MAGIC 



BY ROY BURGIN 



Listing h Atom tfisassefnbfef* 



Eft) ft>IHT'E 



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the cursor by altering the values Mured in 
location* 4 DE and * DF, or if vou prefer, 
222 and 221. Trv this: 

Y- 127 

A -127 

FOR l = *9Q0Q TO #8180 STEP \2BJ222~ Ijl 

LINK* FE2€;NEXT I 

This routine will turn x he screen while in a 
fraction of a second and appears 
instantaneous. 

Have fun experimenting with these routines 
bul be warned, using pieces of code Like this is 
like reading something qui of context si ad odd 
things may happen, For instance, if you cause 
ihe screen io scroll while ihe cursor is not at 
the bos torn of the screen > anything already on 
the bottom line will not be erased but will be 
copied into the next line. 

If you have not made the cursor invisible by 
Typing 

you may leave the odd white square at the 
previous cursor position. 

The demonstration program given in listing 
2 shows how the scrolling routine works. It is 
only a demonstration but it illustrates the 
principle satisfactorily. 



l«1 

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1*4 
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-IVftvf. 



Listing 2. Demonstration program. 



257 ws + c^P. -flTfl*-*.t 

2*1 OGS*IO.F- + -LW-.&,fr 
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ii54 ijOS.t.P-aDVVt, I 
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PPOURHN' 

SCREEN " 



UHSCROU-ED 



LINES IN V 



109 P # *12 W DEMONSTRATION 

129 P. M PRRTLV SCROLLING 
160 REM REMOVE THE CURSOR 

i@o ^#Ei-e 

£26 REM SET NUMBER OF 
240 REM V= (NUMBER OF UNSCROLLED LINES+1)*32 
^59 REM V«C6+1) #32=224 FOR SIX LlWES 
260 V-224 

300 REM PRINT SOMETHING ON ONE LINE 
320sFOR 1-1 TO 3 
340 P,RNE';a*3G) 
NEXT I 



/ J / f /■ / ^V f 4? -#f ^V 



360 

4£3 
4b6 
489 
52fl 

546 
58S 

see 



10;««it;hext 
IT 



J 



REM DELflV 

FOR 1=1 TO 

REM SCROLL 

LINK#FE0R 

REM MOVE THE CURSOR EflCK TO THE STftRT OF THE SttME LINE 

p.*ir 

REM GO ERCK HNC F'RIHT SOME MORE 
OOTOs 



YOUH COMPUTER, DECEMBER 1301 57 



Qualify support for; 

ZX80 ACTION! 

F ticker free action games for your ZX80. need 

only IK RAM and the original 4K ROM. 

Cassette CaOA. BRKOUT . . , AGKACK 

E4.00 

Cassette C80B SHELL GAME - 

INVADERS £4.00. 



ATOM 
ZX80 
ZX81 



The ZX80 Magic Book * WITH BK ROM/ZX81 SUPPLEMENT * 
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much more £4 ?B 

Getting Acquainted with your 2X81 E4.9S 

Mastering Machine Code on yowr ZX8QT 81 C5-9S 

23-23 WAY ZXS0/81 EDGE CONNECTOR SOCKET £360 

23 -23 WAV ZXSQJ81 GOLD PLATED PLUG EXTENSION C3,50 
ATOM CASSETTES. fi each 

CAAAj BREAKOUT - CUPBALL - 3D MAZE - SIMON 2. 
CAAB; PINBALL - LETTERS - SPACEWAR - OftlVE 
ftolh tapes need IK VDU - 5K text RAM 
The ATOM Magic Book 

A wealth of games and other programs; storing speech in your 
ATOM, converting programs written in oiher BASlCs, tape 
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ups. E550 

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Single Eurocard F can fit inside ATOMs case. Built and tested. Bare 
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ALL PRICES INCLUDE U.K. PErP - VAT WHEHE APPLICABLE 

TIME DATA LTD. 

57 Swallowdale, Basildon, Essex 



Can you become a carpenter without a chizel 

ZX-81* 

PROGRAMS ON 

PAPER 

£2.00 each (inclusive) 

ZBO MACHINE CODE LOAD 
Load your machine code fasr 

Features: 

• HEX code input. 

• Decimal augument input, 

• SEmple load address input. 

Z80 MACHINE CODE EDIT 
Debug your machine code fast. 

Features: 

• 3 byte break pdnt 

• Report the contents of A, F, BC. DE, HL and PC 
registers at each break point. 

• Read /amend machine code, 

• Restart machine code routine from the last 
break point. 

Michael Cox Information Services 
G2 High Road, North Weald, Essex CM16 6BY 

■ We thank Sinclair Research Ltd. for permissEon to um th^r 
product names. Thfi companies are in no other way f elated. 



ZX80/81 HARDWARE/SOFTWARE 



2K RAM Pack 

4K RAM Pack 

16K RAM Pack 



£15.95 
£22.95 
£42.95 



16K RAM Kit 
ZX Keyboard 
16K Software from 



£32,95 

£27,95 

£3.95 



RAM PACKS. All RAM Packs are supplied built arid tested, and simply plug into your port on the rear of 
the computer The 2K and 4K RAM work with the onboard RAM, example 4K^ Onboard = 5K. 
KEYBOARD. A full size keyboard for the 80/81. The keyboard has all the 80/81 functions on the keys, and 
will greatly increase your programming speed. It is fitted with push type keys as in larger computers. The 
keyboard has been especially designed for Sinclair computers and is supplied ready built. It also has facilities 
for four extra buttons which could be used for on /off switch reset, etc, 

DEFLEX - £3.95. This totally new and very addictive game, which was highly acclaimed at the Microfair, 
uses fast moving graphics to provide a challenge requiring not only quick reaction, but also clever thinking. 
One and two player versions on same cassette. 

LIFE — £3.95 + Uses M/C to achieve a processing speed of three generations a second on a 20 > 32 grid 
with a superbly flexible cofony editing system. This is without a doubt the best ZX Life available, 
3D/3D LABYRINTH - £3/95, You have all seen 3D Labyrinth games, but this goes one stage beyond; you 
must manoeuvre within a cubic maze and contend with corridors which may go left/ right up down, Full 
size 3D graphical representation. This Program is written in MC/ BASIC* 
All above software on one cassette at £5.95, 

CENTIPEDE — £4.95, This is the first implementation of the popular arcade game on any Micro anywhere. 
Never mind your Invaders etc., this is positively stunning. The speed at which this runs, makes ZX invaders 
look like a game of simple snap. This Program is written in MC. 
Please add £1,00 p&p for all Hardware, Software post free. All our products are covered by money back 

guarantee. 
Specify on Order ZX80/81 

cK'tronics 

23 Sussex Road, Gorleston, Gt. Yarmouth, Norfolk 
Tel: Yarmouth (0493) 602453 



56 YOUR COMPUTER, DECEMBER 1961 



IK ZX81 



T 



GROWN UP GWfS FOfi JADED MINDS All ORIGINAL AhWAJED 
GRAPHICS fXOUISiTE BAP U^f NOT J Oft THE . SOUEAMW 



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Hitler 



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...» IM_ ■*'■-: , 



oSl 






*ll TI*SI FfKXtfAMS' ON CASSI Tf 
fNClUHNG I i RtVQltNOV 

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YOUR COMPUTER, DECEMBER 1981 5B 



PROJECT 

COGENT STEPS TOWARt 



In the previous part of his 
series, John Dawson began to 
outline an interpreter for the 
6502 microprocessor. He 
continues with an analysis of 
the most suitable language 
level and some fundamental 
subroutines, 

LAST MONTH, I discussed the d inference 
between compiled and interpreted high-level 
computer languages and gave some building- 
block subroutine* as ihe start of a control* 
orientated interpreter for the Tangerine 
Microtan or Micron computer. Programs need 
names and Cogent seems appropriate for this 
project. 

Last year I spent some time working on a 
program called Duncan which was an inter- 
preted language for the Xa&com I micro- 
computer. Figure 1 b a short but typical 
Duncan program. Program instructions in 
Duncan consisted of a single letter to identify 
the main instruction heading followed, where 
necessary* by sulked Inters or numbers. 

These identify either a pan or label, or 
provide a conditional code for a jump or Goto 
instruction and the label to which the program 
should transfer execution. When you are 
familiar with Duncan it is easy to use and you 
can build reasonably complex conirol 
procedures. 

Duncan used reversed- Polish notation for its 
number-handling procedures based on an 
earlier language M6, and could cope with 
positive integers in the range zero to 65*535, 
Eight-bit — one-byte — values could be set to 
output devices or obtained as an input value, 
Duncan had no facility for handling interrupts 
but could be used to poll a number of devices, 
either continuously* or at a defined stage in the 
execution of a program. 

A number of ideas occurred io me in the 
course of thinking about an improved inter- 
preter for the Microtan: first, it seemed 
desirable that the source program should be 
written in Enplish mih as few restrictions on 
the author as possible. A person writing the 
program should be able to describe l he tasks 
the computer would perform using plain 
language and fulMength words. 

The compacted coding used in many high- 
level languages is less relevant now that RAM 
is less expensive and this code will become 
increasingly obsolete as more people become 
familiar with typewriter keyboards. I thought 
that the program should be constructed along 
the lines of simple but recognisable English 
grammar. 

For example, the source program should 



consist of a series or sentences with a constant 
terminating feature — a full stop at the end of 
l he sentence followed by one or more spares- 
It seemed that spaces between words would 
become significant since the transition from an 
alpha-numeric character to a space marks the 
end of a word. Consequently, the names of 
variables and input'ourpui devices should be 
linked by a hyphen when they consist of more 
than one word. 

I thought it important thai the program 
should allow redundant material in the source 
program. In other words, the author should 
not have to formally declare that a word or a 
group of words is a remark to be ignored by 
the computer, The computer should be able to 
look through a source sentence and extract 
from, it the information it needs to carry out 
the instructions contained in die sentence. 

Third, eighi-bit accuracy is entirely 
adequate for the vast majority of domestic 
applications and school or amateur experi- 
mental purposes. However, the interpreter 
should be able to handle large integer 
numbers, both positive and negative, for many 
tasks including signal averaging and other 
scientific applications. 

Fourth, reverse- Polish notation is easy to 
work with, both in programming terms and a? 
a user, Hewlett Packard has built a successful 



(TEST ROUTINE - SR CALL AND JUMP 

BACK} 
. (FIRST NUMBER! ?-A PL P P P 
. (SECOND NUMBEfll > - B PL P 
, £7 

. (FIRST PLUS SECONDS C = ? PL 
JS L7 A,B+ -C ; 
(END] 

RRST NUMBER 479 SECOND NUMBER 50 
FIRST PLUS SECOND ^00992 



i%4Jfff 7, A ryptc&t Duncan program, 

range of calculators around RPN tor good 
reason^ and I thought that I would continue 
to use RPN for Cogent. 

There is a classic dilemma inherent in 
interpreted languages - it" it is easy for 
humans to read and underhand, it will be slow 
for the machine to interpret and execute. 
Duncan ran very quickly because the Nascom 
had only to examine a single character to jump 
to the next induction gioup, 

Identifying an instruction from a variable* 
length word, which requires the computer to 
match a list of instructions and list of input 
and output devices, might slow the program 
considerably. It could even be slowed to the 
point where, while still acceptable for many 
domestic control jobs, it would be useless for I 



acquiring data from many experiments in a 
school physics laboratory. 

The task of writing an interpreter which 
would compress a source program to single- 
byte instructions for execution by the 
machine, re- expanding the compacted code to 
the full source listing \r-: editing purposes is 
not for a part -time amateur systems analyst 
and programmer — however dedicated or 
obsessed. 

What is much more important in the design 
of a language is the framework it provides for 
describing the problem faced by the analyst. 
In other words* a good programming language 
should be capable of helping a user to describe 
what he wishes the computer to achieve — it 
should lead him through the dc^n o: j 
program along a logical route. 

Some of the newer languages such as Pascal 
and A PL hue comparatively simple, coherent 
designs which influence the programmer's 
perception of ihe problem, In this way, the 
expressions Do-Until or Repeat-White 
describe nor ]use a feature ol a programming 
Linkage but a useful Jild powerful -ipp:Oach 

tc investigating and writing a solution to a 
problem. 

Let us now examine an important part of 
any control-orientated program — 2 real- time 
clock ] used the two-psfift assembler from 
Microtanic Software id write the clock 
subroutines and it is an enormous advance on 
the translator/disassembler in the Tangerine 
XBug. 

lite good features of the Microtanic product 
are that: the assembler is very fast; the second h 
and longer^ pass through mote than 200 lines 
of source code took just 4.5 seconds. There is a 
high degree of control over the positioning of 
source and object code and it is possible to 
assemble directly form a source-code tape with 
I he result thai the whole of the Microtan 
memory can be filled with object code. 

The p^eu Jo-ops BYT and WOK allow the 
us? of labels as operands which considerably 
enhances the assembler because it makes the 
object code truly relocatable. There is a 
tantalising mention in the documentation of 
furl her pseudo-op codes to allow the use of 
macro instruction! in the future. 

On the debit side, my comments are mostly 
to do with the documental ion. It is adequate, 
but more examples would have been helpful 
and the layout coutd have been improved to 
make some difficult concepts more easily 
understood, The documentation is printed on 
a dot -matrix printer with no descenders. 
Software of this quality justifies a higher 
Standard of presentation, 

One section describing the use of labels as 
operands to the BYT and WOR pseudo-ops 



60 YOUR COMPUTER. DECEMBER 13St 



)S PROCESS CONTROL 



still gives me problems even though t used the 
feature successfully in programming the real- 
time clock. 

The assembler controls a printer, somewhat 
clumsily, cither by internal software in the 
EPROM or by your <iw.n external program, 
However, The printer can only be used during 
the second- pass assembly or to list the source- 
prog ram labels, and 1 could not find a way of 
listing the source program alone. 

These criticisms 3 re minor — the Tan soft 
two-pass assembler is an effective and 
powerful piece of work, backed up by more 
than 5,000 words of explanation and support. 
The three sections of the documentation — 
"IiitnUafions", "What h a two-pats 
assembler? n and **AIJ the technical stufT — 
will start you off on the right track if you are 
prepared to concentrate. The results of using 
the assembler are shown in figure 2. 

The liming values £$40 in line O053 and 



£S#B m tine 0054 may need adjust me ni to the 
crystal frequency in your own machine, At 
present, the program will measure only 
elapsed time from the moment when the 
program starts to run, 1 hope 10 list jmd-iu 
short routine to set the real time in nestt 
month's article, 

The clock records the week of the year, day 
of the week, as well as hours, minutes and 
seconds, When the program is executed ai 
0400 hex, there should he a one-second delay 
and then the top line of the screen is partially 
cleared and i he following figure* should be 
displayed: 

OOOOOOOO01 

The figures read From the left according to 
the following key: 

WeeklO-511 - Day(0-6) 

Hours(24i : Minutes' Seconds 
Every 50ms. the VIA counter reaches sicro 
and generates an interrupt. The VIA timer is 



then automatically reloaded with the initial 
values and the laming cycle recommences. The 
interrupt diverts the 6503 CPU from whatever 
program it is executing to the dock imerrupi 
CLKINT routine starting at line 107. In the 
course of updating the clock counters > the 
routine displays the current time using the 
CLOD IS and B2D subroutines. The lime is 
updated every second which explains ihe 
initial delay when the program is started. 

The instruction LSR @ is equivalent to 
LSR A and is peculiar 10 the Tansoft two-pass 
assembler, With this except ion t all the 
mnemonics are standard 6502 assembly- 
language instructions. Check the machine 
code corresponding to the assembly instruc- 
tion if you have any difficulty. 

The final program section at line 183 
initialises the clock and starts it running, The 
program then loops and will look for an input 
from the keyboard to display on the VDL\ B 



figure 2, Clock subroutines g&ftefaied by tha MicroTBnt'c Software two-pass assembfar* 



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YOUft COWPUTEft. DECEMBER 1981 61 



Acorn Atom 



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THE ATOM: a bi-monthly magaiinfl for Atom 
u«i"5, containing TESTED programs. Covers 
machine code and BASIC programming. Six 
issues for only £4.50 inclusive. 





ce.oo 

£4.50 
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C5.0D 
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ALL PRICES INCLUDE VAT & POSTAGE 
24 hour answering service on 
051 227 2642 for Access orders m 

PLEASE SUPPLY I 

i enclose a cheque/ PO for £ made i 

payable to Bug^yte, OR debit my Agce&s i 
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Sinclair ZX81 

ZXAS MACHINE CODE ASSEMBLER Ah hough many people have 
expressed disbelief, we assure you that this is a full-specification ZBO 

assembler Standard mnemonics are written directly into your BASIC 
program. Code may be assembled anywhere in memory. Handles 

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ZXDB DISASSEMBLERS DEBUGGER The perfect complement to 
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FOR 16K ZX8t &BKRQM ZX8Q - ONLY £5.95 
MULTIFILE A mult i purpose menu ^ driven filing syslam supplied Of* 
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FOR 1GK 2X31 & 8K ROM ZX80 - NOW ONLY £1Z50 
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STARTREK for 1GK ZX81. AH the usual features: r»ine levels of play 

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THE DAMSEL AND THE BEAST A fanta&lic adventure game for 
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Two programs far (he- expended ZK81 to keep 
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MARS RESCUE 

BOTH PROGRAMS FOR ONLV £4 50 

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Connects direcrtv to TH5-B0 Level 2 Keyboard, Operating and 
Ht% hsndJ tn saUwar* m ROM, S commands add 12 power (liJ 

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ctinirgls, Full control ol #>l Junction* from Keyboard or 
program. D?i$v chain multiple rjnues Certified digital cape m 
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Telephone 
0525 371393 



'Ltd. 
24 Heath Road, 
Leighton Buzzard, 
Beds. LU7 SAB 



02 VOUfl COMPUTER . E C€ M BE ft 1 981 



Do you have a problem? Your manual is 
incomprehensible or you just cannot get the 
hang of that programming trick you tried — 
whatever it is, Tim Hartnell will do his best to 
answer your queries. Please include only one 
question per letter and mark them "Response 
Frame". 



RESPONSE FRAME 



CODE BOOKS 

■ I should very much like to 
know if any bnoks c*iM dealing 
with the vexed que si ion of ZX-BO 
machine code — preferably for 
beginners. I have seen the mJd 
machine-code routine, but no 
explanation about how ip enter 
it. or reserve space in the RAM, 
and tiicle tu explain what the 
Pushing and Hanking actually 
do. 

Michael P#k? t 
Bexle\\ tfrof. 

Books quick could help you 
include: Machine language pw^ram- 
ming made stmpk, £&\95 and EAdbr 
Handing your ZX>81 ROM, by Dr 
Ian logan* £8,95, Both arc available 
from The Essential Software 
Company* 47 Brunswick Centra 
London, WO. Mastering wa<hi*tt 
code on y&ur ZX-81 a r ZX-8(K Tony 
Baker ^ £5.95 is available from 
Interface, 44-46 Earls Court Road, 
London* W8 6EJ. 

CHESS CHOICE 

■ Interested in microcomputers 
and as the owner of a chess 
computer, I particularly enjoyed 
the article by John White on 
chess computers in the August/ 
September issue, t wish to 
exchange my chest computer for 
a more powerful model and 
thought it might be a good idea 
to buy a microcomputer with 
such a chess-playing capability. 
John White stated that the 
Morphy 3,5 program was written 
on only SK ROM and IK RAM. 
The Sinclair ZX-81 also is 
advertised as having UK ROM 
and IK RAM, Would I be mis- 
taken in thinking chat such a 
powerful program as the 
Morphy 2.5 could be written for 
use on the Sinclair ZX-81? 

JSStrangty 

As a fiRtEiXAL rule* 1 would suggest 
that a chess program for a micro- 
computer is unlikely to play as well 
as a chess machine. The Morphy 
program you refer to h written 
entirely for chesi, thai is, the 
memory is totally dedicated to chess, 
whereas the same memory on h say, a 
ZX-S1 is required to do many, many 
things, When u chess program is 
used with a computer, ii uses only 
pari of the computer 4 ! capabilities. 
John White suggests in his article 
that the Sargon 2.5 ts the best chess* 
playing machine available, and — if 
you arc serious about chess — is a 
bencr buy for that purpose than 
buying a computer and I hen buying 
a chess program for it. However, 



when you have a computer, you can, 
of course, do far more with n than 
lu*l play chess, One shop which 
carries a number of chess computers, 
where you can compare their levels 
of play, is the Silica Shop, 1-4 The 
Mews, Hatherley Road, Sidcup, 
Kent; telephone 6 1 30 J JUL 

2X81 BUG TEST 

Wj hue-; HBi ".EivEu a number of 
questions about a bug in the ZX-81 
ROM The bug: appears when deal- 
ing with very small, or very large 
numbers, and is especially evideni 
with some Loh functions, and raising 
number* less than one — such as 
viL.iT.ni: 0.125 — to a power. The 
bug in the ROM has been located. 
We believe three extraneous liric^ in 
She Original ROM have simply been 
deleted, a discovery made by Frank 
O'Hara in J aimfirrned by Ian 
Logan, Sinclair Research is now 
swapping old KUM& fur new. If you 
ring Nigel Brown on 0276-62 EH. he 
will tell you how to go about 
obtaining a modified ROM. If you 
decide to buy a ZX SI from W II 
Smnh, test it firsi to sec if ii has a 
KOM-wiih-bug by entering I be 
following line: 

PRINT .125^2 
Any answer other than I he correct 
one — .015625 — shows the com- 
puier h;i* an old ROM in it. Sinclair 
Research tell us Thai only new RCLVH 
are now on the market > but it has 
adrr.it [cd thai a few old ROMs may 
still be m circulation. 

POOLS SYSTEM 

■ I was delighted to read your 
first issue, particularly the 
ZX-fl 1 review. Unlike others, you 
do not hesitate to find fault, and 
I (rust you for this attitude. I urn 
interested in football pools, and 
to date have Laboriously ton* 
ducted research by hand* which 
covers the data of 15 seasons 
with 42 matches on each of the 
season's SS playing days — no 
mean effort, f would tile your 
opinion a* to the best computer 
to aim at, Obviously I cannot 
run io an IBM or similar. Would 
you care to matte any 
suggestions, please? 

Rvbcrt Mamn r 
Pickering ftforri Yorkshire. 

Yov DO not Actually say what you 
wish io do with the computer in 
relation km he pools, but we imagine 
you wi*h to be able to compare, 
analyse and predict. The volume of 
data is taihet large, hut could be 
handled in one-year chunks by a 
ZX-fll with IfiK fit" memory, or any 
small microcomputer of similar 



capacity. However* to handle all If 
years al once, to be able to call 
anything from thow 15 yearn al with 
would require much more memory. 
A disc -operating system would 
possibly be an idea, if you really 
must have ail 15 years on lap at any 
one time. A £1 football-pools, pro* 
gram is available for the ZX-Bu" from; 
J'eter Va«y* 1& Kerndak Grove, 
Ease Boldon, Tyne and Wear. 

VIC DOWN UNDER 

■ l would J Ike to pose a question 
regarding the Vic-ZQ, 1 read in 
your magazine the Vic-20 has to 
be tuned to suit the differing 
sound channels and TV 
standards- I will be buying a 
Vic-20 soon* and hope to build it 
into a larger system with all the 
peripherals. The trouble is thai 
in a few years I may go lo 
Australia. Would 1 be able to 
adjust the Vk-20 to suit the TV 
or would I have to sell the 



system? 



Paul Orwmtdt-Jflwe§ r 
Si Altenh H*rrfard$kir& 



The Australian ickrmon system is 
fatty compatible with the British 

system, so you will have no 
problems. You can find out more 
about ihe Vic from distributors, 
which include the Bvtethop, 01-387 
0505. and The Vic Centre, 01-992 

BOARD CONTACT 

■ I am interested in chess 
programming* but do not ln»w 
where to start. E am a pro- 
grammer by profession and my 
favourite language* arc Batte f 
Cobol and Fortran. Please let 
me know of anyone who has 
written chess programs in this 
part of the world, Perhaps we 
could meet and help each other, 

}&hn Kay, 
LagiH, Sigtria. 

w 1 !- im not know of anyone in your 
pan of the ^lobc who has worked on 
chess programs! but suggest that one 
way to contact people who>have 
done so icl the U.K. would be to 
write to a few of The smaller firms 
advertising chess programs. These 
jre : i u>s i lively to have been written 
by the people running the company* 
and they may be able to help you. 
AltOt you could buy -some of these 
programs, to analyse Them. Dm ml 
I his may give you some ideas for 
writing your own. 

COMPROMISE 

■ During the past month I have 
had limited access lo a 
Commodore Pet, During this 
rime 1 have acquired some 
programming skills, and E would 
now like to buy a micro for use al 
home. The Pet is out of my price 
range, Perhaps you would 
advise me about which 
computer would incorporate the 
features listed and would jtfvc 



me the best value for money; 

■ Reliability with software 
available. 

■Cassette loading using existing 

cassette player, 
■Expandable memory. 
■Good formal size with good 

i;j-.i p h i l >. for drawing 

purposes. 
■Should cost not more than 

£200. 

A Birch, 
Tufftey, Gieueanr. 

L'sJ uk: L'naj i-l v, your demands axi: 
incompatible. The Vic-20 would 
enable you to use, almost wuhtiui 
modification, the programming 
*ksta you have picked up on the Per 
and also has expandable memory. 
There is soft ware available for it and 
the machine costs around £200, 
However* you need the special Vic 
cassette player — £40 to £50 — and 
the graphics as supplied arc coarse. 
If you are prepared to spend up to 
JL 300 or £350, a number of suitable 
machines are available, including the 
HIJC Micro, Tangerine. Video 
Genie and the like. If you have 
limited money, your purchase will 
have to be a compromise. - 

SANITY SAVER 

■ Can you please save my 
sanity? I am 14 «ind scilcl my 
ZX-S0 hoping to save up for a 
Vic-20. when a friend suggested I 
buy the whole 2X-8I Ml — 
memory* primer, computer — 
which would be the same price. 

Ann I her Irie-ni) proposed an 

Atom or L'KlOl, and my father 
advocated a SupcrtoanL Please 

lou Id you help and £uidc mc> 

DJAbrs* t 
Cadishtadi Ma whaler* 

Rons'FV 2A£5> of Sybex telli Your 
Computer thai the trend in America 
nowadays is Tor people so work out 
what i hey warn to do with their 
computer, and then buy one which 
fits thai specification, We can only 
suggest you do the same. The 
questions you will need to have clear 
in your mind when deciding what to 
buy could include: 

■ How much money do 1 have to 
spend? 

■ \Vhat graphics quality do 1 want? 

■ What do 1 want to do with it? * 
for EXMnpkp play Space Invaders; 
program in machine code, in 
Basic; control external devices like 
lights. 

■ How much memory will 1 need 
for thi^> 

■ We 13 I he likely to want to add a 
printer or other peripherals? 

■ Docs tt need an external cassette 
machine or has it one built in h or 
will ii require floppiest 

■ h the computer generates a colour 
picture* do 1 have access to a 
Colour TV to make use of the 
colour facility? 

Ask your self these questions, 
putting the answers in writing* then 
try and find a machine ro march yam 
answers. B8 



YOUfl COMPUTER, DECEMBER 1961 63 





WILTSHIRE 

SPECIAL OPENING OFFER 



* LOWEST PRICE ' SHARP MZ80K 

20K Machine only £365.00 

16K RAM upgrade (including fining) £4250 

Also in stock - VIDEO GENE at £299.00 

VIDEO GENE II at £235.00 

Sound Kit £10. QO Colour Board Kit £35.00 

+ AJ + Colour Computer - 48K + Stereo Sound only 

£595.00 
Centronix 737 Printer £359.95 
Software — Books — Service 
Orders accepted by telephone using Access or 
RarcJaycard. Postage £9.00. 
Credit terms are available. 

Please add 15% VAT to all prices 
Orders now being taken for Vic 20 

VISIT the Friendly Computer Shop 



d 



veryman 

omputers 




14 EDWARD STREET, WESTBURY, WILTS. 
Tel 1 0373) 864644 Home Tel: 623764 



~~1 



Open all dav Saturday 





ZX 81 owners 

Protos 

Keyboard is here! 

At last! A rpcil full size keyboard in a top quality case for 
your ZX 81. 

Simply unscrew your ZX 81 printed circupl board from its 
black Sinclair case and plug into Protos. 

FULLY BUILT £64.95 inc. VAT 

m More accurate, faster typing wrtti bigger and reafk&y* 

• 40 colour coded key- tops (or e*$y reading 

• Robust, "big" computer construction 

• PC6 prepared for more add-ons to come 

• New edge connetior provided for Sinclair and other 
manufacturers' peripherals 

• Key fegends can be changed for future new ROM functions 

• Sincfair PCB fully enclosed - and room for much more 
If you feel you've outgrown your ZX 81 don't sell it for 
peanuts and move to another system, Add it to Protos 
and make your ZX 81 grow. 

For details, Large SAE, please, for orders add C2.50 posl and 
packing. Cheques to 'Frame Computing' . 



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Computer 

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Computing, 

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F X 702P 1 


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£ 


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m 


— 2 -J 

ran 


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■ 


Erra] E^ 


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m 


m 

— TIE* 

m 


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Ol 


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IS B 


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the FX702R A pocket computer 

that communicates 
in BASIC language. 

AVAILABLE AT SPECIALIST CASIO CALCULATOR OUTLE S. 



Hand held alphanumeric 
programmable- BASIC 
language- holds up to ten differ- 
ent programs simultaneously - 
subrautines nested up to ten 
levels -program looping up to 
eight levels -simplified program 
editing and debugging -variable 
programming capacity: between 
1680 steps with 26 memories and 
80 steps with 226 memories- 
55 single key routines including 
log, trig and hyperbolic -built-in 
routines include standard devia- 
tion (both types}* regression 
analysis and correlation 
coefficient -ait programs and 
memory data retained even when 
switched off Chmpreh&mzw lihmry 
zvitfi ova- 70 program examples. 
Qp£kmaIFA2 adaptor for prttgrmn 
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WHAT WILL THEY THINK OF NEXT? 

CASJO ELECTRONICS CO LTD., SHA1BURN HOUSE. 28 SCRUTTOM STREET, LONDON EC2A 4TY 



64 YOUR COMPUTER, DECEMBER 1981 



FINGERTIPS 



Fingertips is our regular calculator column 
covering calculator news, programming hints 
and examples of unusual applications. The 
column is written and compiled by calculator 
enthusiast David Pringle who is glad to hear of 
any of your Ideas. Your Computer pays £6 for 
each of your contributions published. 



Foft cased- to release its third mafor 
line of calculators in a year — a* U 
ha* done with the Casio 702- P, cakes 
some organist icm T in both senses of 
ihe word. The 702 provides the firsi 
opposition to the Sharp POI2I1 
and Tandy prugrrtrnimbie-s in that if 
uses Basic and has simitar cap- 
abiiiiies. Table ] gives a check list of 
the more impart am characteristics. 
Robin Terry of Barking provides 
us with our first Basic program of 
[h.^ coluclir.: Kaldh ni O^mi — -> 
a game which is played widely in 
Africa, he writes. The pSayin^ area 
consisrs of two rows flf six pas in the 
ground, each filled with five stones. 
There are two pits 10 the sicte N such 
thai the board looks like this: 
Player l 

UOODDD 

12 3 4 5 6 O 

OQOOOO 
Player 2 

The large pit on the player 1 ! ri^ht 
h called his Kaiah. To play^ a player 
chooses a small pit on his side, and 
removes alt the stones, holding them 
in his hand. Then, one by one, 
moving anti-clock wist he drop* lrle 

stone? m successive pits — includanp 

his ov>'n T hui no: ru* cYpprtppni's 
Kalflh. If he holds enough stones, he 
will drop them into his opponent"* 
smaller pits also. Then his opponent 
follow* iuit. 

If, however, the East stone a player 
Jnys :.i-|v i:\ : his ov ; KJjk. :i<: 
then earns another turn. Also* if rhe 
las? ssone falls into an small, empty 
pit on his own udt.\ he may en- ■■■■■, 
[he small pit directly opposite on hjs 
opponent's side and r together with 
the winning stone, drop them inti'i 
his own Kaiah. The game continues 
in this way until a player cannoi 
play; then the player with most 
scones in his Kalah wins. 

In reply to my request for 
information on methods of matrix 
inversion, Boris Allan of Stockport 
writes: It has been found by a 
correspondent to Fingertips — Billy 
W.^U worth. Your Cvmpuwr Aupist/ 
September — that the Cholesky 
method of matrix inversion is not 
always satisfactory — sometimes 
there is an attempt to take the square 
root of a negative number. The 
Cholesky decomposition meihod is 
used to invert symmetric, positive 
definite matrices — that is* matrices 
which arc symmetric and have a 
positive, non-aero determinant, 

To attempt to take the square root 
of a negative number during the 
decomposition suggests thar the 
determinant is negative Or zero. In 
this situation one can exercise 
various- options, of which the three 
most popular are: 
■ Giv« up 



■ UHI rrigti method 

■ Use a pseudo- inverse method 

Let us reject the first possibility 
and try the ihird. 

Pseudo-inverse methods are rather 
more sophisticated in a mathe- 
matical seme. A compact routine to 
produce a pseudo-inverse — usine. 
the Jordan method — is given in 
Magi Test 1 Floating "The :tmi 
value of bench marks 1 \ Pbq&foai 
C&mpuzingi June 19-61. As. Billy 
Wjd'.w'n::':! probably uses the 
Cholesky routine to economise on 
storage — and the Jordan routine 
requires a full mam* — 1 will now 
^ive an algorithm for a pseudo' 
inverse mm hid usn- -lie Cholesky 
method — but what is a pseudo- 
inverse.^ 

This matrix is singular, because 
column 1 and column 3 arc linearly 
dependent — the numbers- in column 
3 are twice those in column I: 



'1 


1 


S 


2 


5 


kg 


M 


1,5 


H 


10 


16 


4 


2 


1.5 


A 


e 



A pseudo- inverse rouiine would 
*mp through l his matrix Y performuiB 
various computations, until it 
leaehed column 3. If the routine 
were a normal Cholesky procedure^ 
it would take the square root of zero 
und then try ic+ divide by ihe aero 
value, or — wkh rounding errors — 
it might rake rhe square root of a 
negative number. 

The p«eu do- inverse routine t how- 
ever, sets the appropriate row and 
column to zero* so thai the original 
matrix becomes 



e. 4 


5 





2 


5 


6.5 





IJ 


:: 











"- 


1.5 


Q 


& 


■md^hiil is 


reaUvinvened 


ts the sub- 


m air iv 








c. t 


5 


2 




5 


6.5 


U 




i 


1.5 


6 





and ihe averse of this maiti* U 
D 365 -27 -5.5 

■5.5 3 1 

This inverse is then substituted 
back into the modified matrix, B. to 
give the paeudo- in verse 



36.6 -27 





55 


-2? 20 





4 


a a 


. 





-5 5 4 





1 



To have rhe problem, as expressed 
by Billy Wadsworth, suggests that it 
i-5 in pan due to rounding errors — ■ 
change in order of the rows and 
columns might then solve the 
problem by noi having perhaps so 
many rounding errors. 

To atcepl a pseudo-in verse i$ up 
to ihv individual, buk in case* here is 
an algorithm for the Cholesky 
pseudo-inverse rouiine. It is worth 
noting thai l he two-dimensional 
array A(n>n) can be simulated by a 
one-dimensional array 
BMn- 11/21 

in the case of a symmetric matrix. 
The cell A(i,i} is then the equivalent 
of the cell 

B«il2n + l-il/2-n + jl 
I have written an Atom routine on 
this basis. Only the lowcr-iriangular 
part of ihe matrix is used in the 
rouiine, so I give ^hc example marrix 
and alter each si age the new contents 
oi slire malris so that you can check 
!;he translated algorithm. 

taout matrix 4 5 2 

5 6 5 1.5 

2 1.5 6 

f continued on fi&xt p&gel 



Tabfe f. Comparison af Sn#rp PC- 7-27 7 ....-.,■; Casio 702- P 




#=> 



gf^Saga^** 



\ 



fgassw- 




Sharp PC 1211 
Tandy 

Price 

£79.90 from Compshop- 

London 
Keyboard 

QWERTY 

57 keys 
Display 

24 character severvby-five 

dot matrix,, 10-digii manti&sa 
Memory Non-vofatiio 

Usor-dntmable: 

From 1,424 program 
steps/26 memories to 20S 
program steps 
178 memories 

All standard scientific 

functions except hyperbolic 

and statistical 
Arithmetic 

15 levels of parenthesis 

priority as irt standard Basic 

Maximum subroutine nesting 

= 4 
Accessories 

CE-121 cassette interface 

CE-122 printer 



Casio7D2*P 



C1 19.95 from Ternpus- 
Carnbridge 

ABCD 

65 keys 

V 
20 characters of similar type 

No n- volatile 

User-definable: 

From 1,680 program steps. 26 

memories to SO program 
■steps v'226 memories 

All scientific functions indm 
linear regression and standard 
deviation 

20 levels of parenthesis artd 
priority as in standard arithmenc 
MaKimum subroutine nesi 
= 10 

FA-2 cassette interface 
FP^IO printer and ROM paefcs 

^re available next year 



VOUfl COMPLTT£R, OECEMBEfl 13S1 m 



FINGERTIPS 



5 £ tones/Pit 



1 print n; w C lp ;a; bioidiei+i "(mine)" 

2 i*r i nt m ; I ; k ; j < i ; h .; " > " ; « :< " < yours > " 

3 return 

5 t=@ -for ^Stol3: t=t+Ca(^K>0) : next ci 

6 return 
IB n W* clew- P3Juse"Kalah pro-straffi by R. terry" : pause" 

to start. " 

15 tor *t = 1 to b ■ a<oO = 5 : a <c*+7)=5 next *t : siosub 1 

17 r:-ause "Luhen you osnt move^ "pause" enter when asked" : pause 

""<uihat Pit?: 11 

£0 inK'ut "6-i start.- 1 - you start" ;s : its **Gto 115 

25 beep i- pause "my ^u" 

3G u=0:for *-i to 6^(^26)^1 

32 it a (^i>=0 scrto 65 

it a (o0>u let LF*a<<*) 

ui=-:t-a.< *D > u"=14* <. \x< 1 > +IJJ - w= w~ 1 im s 7 > " k-=*l+26 

it w=14 let a <p>=2 b 5 = ^oto 65 

a(^>*aCp>+tACot>=u) 

a<P>=a^P^ + (a<^i+l >-D#(fliOS> 

5Ap:)-aO:'::- + ^aXw>=3>*(w>7> + <a<w+l> = l>*(»>13> 

a(p)=a(P> + (aCw>=Q>*(m<7>*C3 i i- i4-w)>0> 

next *l = u=l 

tor * - 6 to 1 ste* - 1 - it a (at+2£»u let u=a<d+26> : r =h 

next ci: beep r- it u=0 pause " i cant move Jl ' iioto 165 

Print "i erriPty pit";r ui-r^l 

for ml to a (r) ■ w=14*<wU >+w : w=w-<w=7> 

a< w ) = a< w ) + 1 : w= w- 1 ; next *i & c r > =0 : w= w+ 1 

if C *<«>*!>* Cw<7) letn=n+a<14«m> + l " a(14-m)=0^(nO=9 

aosub 1 : if u.i=14 Pause "my **o aaain" : ^otc 30 



if CK8) + Cr>13) noto 160 



115 beep 1 ; pause "your ao* 

120 input "what Pit? (i-S)" ;r -r=14-r 

125 if a<r)-0 sot© 120 

136 w=r-l for cpl to a (r) - w-14*(w<l>+ui : tv-m- v <w = 14> 

135 a0.y>=a((M> + l : w=w-l : next *t : a(r) = 

145 if (aCui+l) = l >*,<06> let «=s+*<13**p> + 1 = a<13-u<>=0 ■ a<w+l >=0 

150 stosub i r if mi =6 pause "your ^o a^ain" : -yoto 120 

155 ^oto 25 

16© aosufo 5- if t print "cheat! you can moue" goto 120 

165 if 3>n print "you win... this time. .." end 

170 if iKYi print "i win <ha! ha J > = end 

175 print " its a draw- , ■ ■ • " : end- 
type shift K in DEF mode to run 



listing for Kaf&h or Ow&nL 



(continued from prevrovs page) 

Choltfsky Decomposition 

E M,G E-6 ; Criterion tor pivoting 
F-or J ■ l to ft j Go -down each 
coEjrtin startmg at The diagonal 
H J ■ 1 Goto L1 ; The firsT column 

to *li<ih tly Odd 

For K * 1 to J - 1 ; If J ■ 1 then 

J- 1 tennfc « ii kotfd 

aij.j) Atjji a-:j,k:- aij.ki : 

Much fa-attar triari using a power of 

two 

EndloopK 

LI: WAUJJ leu than Ethtn 

AU.Ji -0 : Pivot check, for aqrt 

of negitive 

if A l J, J) more Ehan E tMn 

AUpJJ" t/sqft(A(J # JJ) ; Wofmal 

action 

If J - N goto L2 ; EvOTtnlriQ h» 

finished 

Fof I ■* J + 1 id N ; Mow we ire on 

10 th* off ■ diagonal 



It J ■ 1 goto L3 - Jump Over this K 


AIJJ) « -X« AiJ.Jf ; The imH 


loop 


move 


for K*1 to J-1 s WJ«1 then 


EndioopJ 


J - 1 is mo 


Endloopl 


AIU* ALU) AIIX^-AIJ.KI 


Matrix .9 —25 -5.5 


EndloopK 


-2.5 2 A 


L3: AH, J J - AM. J) x AlJ, J) ; E>0 not 


-SB 4 1 


divide, as rad&roc*! airtedv 




Endloopl 


Forming lnv*n* Matrix 


L2: EndloopJ 


For I - \ to N ; Column 'Wise 




For J ■ 1 W U ; From diagonal 


Matrix .5 2,S l 


down 


2 5 2 -2 


X*0j Temporary 


l -2 1 


For K ■ J 10 H ; flow anti column 




-multiple 


Irwen™ Cho!»iky Matrix 


X»X^AEK,J|xA1K p 


Fw I a 1 to N 1 j Columnwise 


EndloopK 


from 1 to IM ■• 1 


AUJ)»X; That ii rt 


Pat j -r. I * i io N : Th* diigonal 


EndsoopJ 


element n Ok 


Endloopl 


X b ; Tamporafy stor^^ 


Matrfx. 36.75 -27 -SUB 


For K - 1 to J — 1 j Cofiecss a row 


-27 20 4 


and column muUipii 


-5,5 4 1 


X X + A(KJ)«AU,KI 




EndloopK 


If you found that you could no 



quite lift oiVwith ihe flight simulator 

pro^rim :n tht October issue* il mty 
have been due to lines 46 and 57 
which sfadidd ha^ read X*G?* and 
lincfr 171 and296X*Y? 

This month's finisher is another 
small biai!Mea«r, Consider a row of 
four points: 

• • • • 

H >^u ure yt an end then ihe only 
my of moving i^ back towards the 
centie; at the middle points ihe 
pfobJbihu- of going k> the left or 
right s* zxacily equal to 1/2. Suning 
at <sne end, what is the expected — or 
average — number of moves to take 
you 10 the other end? 

The solution is asymptotic, so take 
iw& consecutive answers separated 
by less than 10-* io be the ending 
criterion A year's subscriprion i 
tile most ekgant iOlgttOn. Bi 



66 VOUB COMPUTER, DECEMBER 1*1 



q„ 



th 



FORTH for " 
TANGERINE 



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much interest is NOW available to Tangerine users. FORTH Is 
both an intef prate; and compiler offering the power of a high 
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• A full standard implementation of fig-FORTH release 1.1 
t variable tengTh names and compiler security \ with RAM 

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• Plus hi- line assembly via linkage to the XBUG line assembler 

• Plus a FORTH editor 

• Plus a cut down version offering 8K users (Micron or Microtan 
+ Tanexf increased dictionary space. 

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Documental ian ovists o< the FORTH mode* overview l he FORTH 
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n-^ n^pJennentaicon instructions. A PORTJH primer &r use* manual i* 
recommanctfld for newcomefs The lull imptofnenution tde^ry fequiies 12 
w> 1GK of RAM, although ii will load into SK Ibcil then dictionary space is 
limited and lac* of buffer s.pdce precludes the u$* ol input/ output! , Th* 
cut down version, by excluding i o and related ut^mei defers the BK 
users ejctra dictionary space. 

For ihove wishing to customise th&t own versions, essambtf r source 
code can also be supplied foi an aaira cost of £5. This is suiiebJe for 
assembly by the Miootantc 2 pass assembler EPRQM unpi«meniations 
also undertaken bv request. 

Orders fs&tt fiy refy/n wftere possOOef to. 



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YOUR COMPUTER. DECEMBER 1961 67 



ZX81 



+ 16K 




SPACE 
BATTLE 

Using superb dynamic 
flicker-free graphics, 
this 'Arcade' type game 
with continuous score 
display fs instantly 
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you must escape into 
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succeed, the action 
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STELLAR 



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As a member of the 
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escape safely with all 
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ZX80 



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DRAGON MAZE., .are you cunning enough to evade 
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!h* ruras - th« draflo-n breaks them when he gets 
angry. Fun for all ages ! 
Cassette a*d lisling., C5.00 _■ 




"OUTSTANDINGLY USEFUL" 



THE 

ZX81 

COMPANION 



ESS EP 



STORY. 



Bob Maunder 



LINSAC 



Price £7.95 incL UK postage 
ISBN 907211 01 1 

THE ZX81 COMPANION was reviewed 
in the September 7981 issue of the 
Educatfbnai ZX80/81 Users' Group 
News/etter as foifows; 

Bob Maunder 's ZX80 Companion was rightly recognised to be 

one of the best books published o-. progressive use of 
Sinclair's fFr&t micro. This is likely to gam a similar reputation, 
In its 1 30 pages,, its author does not go as t&t as he did before, 
but his attempt to show meaningful uses of* :be machine is 
brilliantly successful. 

The book has four sections, wiih the author exploring in turn 
interactive graphics (gaming], rnformaiion retrieval. 
educational computing, and the ZX8J monitor. Fn each case 
The exploration is thoughtfully written, detailed, and illgslraied 
with meaningful programs. The educational section is the 
same - Bob Maunder is a teacher - a no here we find sensible 
<deas, tip*, warnings and programs too. The monitor listing 
10Q00 to GCB9L while unique, is less fully backed up r and witt 
be of no use to the ZX3I beginner without some knowledge rjf 
Z-80 assembly. 

To conclude ~ thrs book is definitely &n outstandingly useful 

second step for the ZX8? user. 

Send cheques for £7.95 to: 



LINSAC 



fYCJ 



66 BARKER ROAD, LINTHORPE, 
MIDDLESBROUGH TSS &ES 



68 YOJR COMPUTER, DECEMBER 1381 



BOOK REVIEWS 



The gateway guide 
to the ZX-81 and 
ZX80 

By Mark Char/ton. 
Published by Database 
Consultancy, 180 
pages, paperback. 
Price £5.95. 

On the whole, [his book, 

unsurprisingly, lis] tows, the standard 
Har/mell/Database pattern. It is a 
collection of programs, mainly 
games, with notes on ZX program^ 
ming along the way. That is a well- 
tried andj without doubt, very 
succcsslui pattern — even if it is one 
which docs not add much sptffkle to 
life 

This particular follower or the 
pattern is no better and no wor&e 
than the other*. If you have just 
Started with the ZX-Slj it will [each 
you no more and no less than the 
others. If you are beyond the basics, 
it will give you more ideas for simple 
games, 

Charlton's hook has a few pluses 
— better binding, somewhat better 
layout and accuracy and some useful 
appendices. It does not, however, 
tackle anything serious, there are 
plenty of examples of poor program- 
ming, and there is no index, 

Conclusions 

■ if you have not advanced very far imo 
Bincla^ miCfOCOrnputirvg, This bank is 
as nood 35 any athor iniroduclory 
collection of nrotjrdms for these 
maehmas, 

CH you atroady hava pieniv of material, 
it will not offer much apart from a few 
mora gam* variations. 



Atomic theory and 
practice 

Published by Acorn 
Computers. Supplied 
with each Atom or 
supplied separately for 
£8.00. 

To A newcomer to computing, there 
is one component of a computer 
system which is of crucial 
importance — the instruction book, 
Acorn seems to be aware of this and 
the book supplied with the Atom is 
of a particularly high quality. 

Ie tackles the subject with a 
delicacy of touch rarely found in a 
technical manual, The Inex- 
perienced user is shown that 
programming a computer is 
reasonably straight forward. 

At the same time, the more 
experienced reader is advised to turn 
to an alternative section which 
corresponds better to his interests 
and experience, The book also deals 
with assembly-language program- 
ming, and to make it easier to find 
the chapter required, the book has 
colour-coded sections, 

Most features are illustrated with 



excellent program examples which 
reinforce the text. There are 
additional reference sections, 
covering just about everything you 
need [o know. 

Many manuals cover their 
machines as comprehensively as the 
Atom out, but few are as well 
designed to help you quickly find the 
information you require. An 
exceptional lipase index comes to 
your assistance if con terns page and 
colour coding fail. 

Conclusions 

■ Atom Theory ar>d Practice b the 
hand-bonk against which olher 
manuals should be .udqed. 

A4*fl Tayfar 

Atom Business 
Published by Phipps 
Associates, 3 Downs 
Avenue, Epsom, 
Surrey. Price £6,95. 

"['IMS R'i-ik is mosl Lnie:eMiri£ and 
unusual. As the title suggests^ it 
contains business pi o^rdu is and ;ht 
most notable ones are the nominal 
ledger system and the pair to keep 
sales records and plot the results 
graphically. 

The book would be of most use to 
someone with a fully-expanded 
Atom Liiid j printer, but there are 
items of interest to most Atom users. 
For example? in the sales graph, a 
technique is shown for mixing text 
and high-resolution graphic*. Addi- 
tionally., ways are shown to save 
large amounts of data to cassette and 
read them as required. 

The programs for the most part 
arc menu-driven and easy to load and 
use. They do their jobs very well and 
che book includes some useful tips 
and explanations. 

One particularly noteworthy fea- 
ture i$ the way that each program 
has its own chapter, divided into 
three parts . The first part explains 
what the program does, the second 
explains how to operate the program 
— usually including a sample run — 
and the third pan gives the listing 
and explains how the program works. 

Conclusions 

■This booh is particularly Appealing as 
it shows how the A;om cen do user" ul 
jobs rather than juii play games. 

L.Vefy few boots show how to us? 

popular computers in s&nous ways, 

end Atom users. en lucky to have a 

work of This quality at their disposal, 

Attn factor. 

Video /Computers 

By Sippi and Dahl. 
Published by Prentice 
Hall International. 
Price £5.55. 

This is a frustrating and eventually 
worthless book. The full message on 
the front cover is: "How to select, 
mix, and operate personal computers 

and home video systems 1 *. 
The concept that in format am 



technology is spreading imo people's 
homes and that it is desirable ior the 
hardware to converge into one grand 
informal ion terminal is faulck-ss; it is 
only the book itself which is flawed. 
There arc many illustrations in the 
book, all of a typically American high 
standard, bait the caption* appear to 
be taken directly from the martu- 
facturer's advertising material. "Why 
do you need nine piaure* of colour 
TV cameras one after another for 
any purpose apart from filling space? 

The book fails to carry through its 
theme and there is no serious 
discussion of how a system might be 
assembled and no mention of the 
major problems of incompatibility 
both at an electronic-signal level and 
at a data-transmission protocol level. 

You will be interested to know 
that the Sinclair ZX-80 is described 
ihus: "Despite these minikin 
proportions, it docs every thing rhat 
larger * more expensive home com- 
pute ts do". 

There are factual inaccuracies as 
soon as the book drifts away from 
the material supplied by the makers 
of j host of hardware. 

Conclusions 

■ h vou want your imagination 
stimulated and lulled with accurate, 
up-iD-dace inlorrnation on I ha- silicon 
'avoid tion, this is not the book to do 
ii 

■ l regnei The loss or Iht trees, which 
were pulped and watted tor tha 
printing of Vidta/Cempuien. 

John QftwsoH 

Mastering machine 
code on your 
ZX-81 or ZX-80 

By Tony Baker. 
Published by Database 
Consultancy, 180 
pages, paperback. 
Price £5.95. 

WkULI If is possible 10 prepare good 
ZX programs in Basic, it is not 
possible to do so with full efficiency, 
high speed and high effectiveness, 
This book is an exceedingly brave 
attempt to introduce the thousands 
of XX novices to the effective use of 
machine code. It consists- of 130 
close -packed pages of text and 
routines through which the author 
adeptly leads the diligent reader 
from first steps to a complete under- 
standing of the subject. 

The reader must be diligent, 
though. There is little poini in 
skipping through until one finds 
some exciting routine and tries to 
enter it, 

One must work at machine code, 
step by step. One must also be 
diligent to overcome the Tew errors 
in The book's first real machine-code 
program. 

To use this book properly — and 
by the end of it be able to write long, 
useful programs and routines — you 
need to give yourself a solid week in 
the Common Cold Research 
Laboratory h Yet even after three or 



four hours — and with the benefit of" 
some background knowledge — I can. 
now work through published 
programs and see what they ^rt 
intended to achieve. 

In those ISO pages we find all 
kinds of techniques which should be 
used in eommefuial c#*.se«es- The 
main theme is a JK draughts 
program. There is also material on 
character generation, keyboard 
scanning, making musk, displaying 
a series of pictures at speed, 
disassembly and arithmetic. There 
are game* and serious routines, and 
the final program is a delight. 

Conclusions 

■ A beau hfiilly-sTrueiu red guide 1or Tine 
unimiipiad which pulls no punches 
and yet which .s assy to use. 

■ it contain* planty of useful machine- 
code routines and programs. 

■ if you can tor-era I e ihe poor 
presentation and tmy type — 1 he end 
result is a new world. 

Eric Deesvn 

Getting acquainted 
with your Acorn 
Atom 

Published by Database 
Consultancy, 105 
Fairhoime Avenue, 
Gidea Park, Romford, 
Essex, Price £7,95. 

Tins work has fallen into the trap 
which has claimed so many victims 
among computer volumes. Books 
written as complete programming 
courses, in which you follow 
examples to master the computer, 
always duplicate material contained 
in the manuals. 

The siyle of this book is to give a 
program listing in sections, with 
explanatory comments about what i$ 
happening. A cynic might suggest 
that this is a way or making 4oz< of 
programs fit a 31b. book, but the 
comments may be of great interest to 
some readers. 

My greatest reservation it that the 
examples given have a large number 
of errors in them. Most arc of i 
minor nature, but in a book which 
assumes negligible experience on the 
part of the reader* such errors should 
not be present. 

Many of the programs were 
originally written for oihc= machines 
and have been converted. This 
meant they do not tike advantage of 
the Atom's programming strong 
points. We are even told lei use the 
Stop command — the Atom does not 
have one. 

Conclusions 

■ The jo are «m* good thing* to be 
said for the book: it gives you many 
idea* 10 try, and 4 he style may bo just 
what some people need to help thtffn 
on their way to writing thoif own 
programs. 

■Perhaps lhe best advee is to look at 
this book m a shop and W c Far 
vourasH rf m *s what vou need. 

Atin Tsytor. I 



VOUR COMPUTER, DECEMBER 1981 3& 






UK 101 
TRS80 




SHARP 
ZX80/81 



MICROTflAIN 

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70 YOUR COMPUTER. DECEMBER 1961 






SOFTWARE FILE 



Software File gives you the opportunity to have your programs, 
ideas or discoveries published. We will accept contributions for any 
personal computer and will group programs for like machines 
together in the file. Please double-check your listings before sending 
them. Mark your letter clearly for Your Computer. We will pay £6 for 
each contribution published, 



Machine-code tips 



m<*m 



W £ Thomson, 
A/dsburgh, Suffofk 

Trevor sharples' article in the 
August/September issue did not perhaps draw 
a sufficiently sharp distinction between 
working with the ZX-80 and ZX 8L 

For example j in talking about putting 

machine-code programs in Rem statements, he 

said: 

Do not list [he Rem statement. Somes imes^ but 

not always this will cause the ZX-80 JB I iq crash. 

True enough, but the statement hides the 
vast difference between the machines. One- 
quarter of the character codes — those from 64 
to 127 — appearing in a Rem statement listed 
by the ZX-80 cause chaos. The ZX-81 is much 
more placid: only 118 and 126 bother it. 

They lead to corruption of the listing in 
degrees of severity varying from she omission 
of six characters within the REM, to a listing 



that stops half-way through the Rem. There is* 
however, no crash; only the listing is 
corrupted and the program can be run without 
trouble. 

The other example is the renumbering 
routine. The text has: 
The ZX-IWS1 will then execute line 9070, 

This gives the impression that the routine 
can be used for either machine, whereas it can 
be used only for the ZX SO, This routine 
advances from line to line by looking for 
character 1 18 — Ncwline — knowing that, 
apart From the line number nsc!f T 118 can 
appear nowhere else in a statement. 

In the ZX-81, however, 1 18 can also appear 
in the bytes the listing dots not print — 
namely, those that give the texi length and 
those that give the binary form of numerical 
constants, A ZX-81 renumbering program 
must use a different approach. 

My program uses the texi length to skip ro 
the end of each line. It also detects the end of 
program by looking for the address where the 



display file starts, so there is no need to have a 
9999 line in the program 
A possible loading program is 

1606 LET fl- (address of 

1st byte o-f i*roi*r-am> 

TO fl+36 



luwl 


FOR I=R 


1002 


INPUT B 


1803 


PRINT B, 


1004 


POKE X,E 


1005 


NEXT I 


1006 


CLS 


106? 


RflNIi LISF 


1003 


LIST 



This differs from that associated with the 
ZX*80 renumbering program but the dif- 
ferences are not vital — just a matter of 
individual preference. 

The program renumbers in steps of 10, but 
only one byte need be changed to alter this. 
Instead of 10 — about half-way down — use 
whatever you want. Or> if the routine has been 
loaded, Poke A+ 17^i will make the change, 

It may be as well to remind you ihat such a 
renumbering program does only half I he job. 
The arithmetic expressions following Gotos 
must be altered by editing to agree with the 
new numbering scheme, with possibly other 
changes. 



Bytes in decimal 



by mho lie Instr 



33 124 


64 


17 





35 




237 75 


Id 


167 




237 66 




200 




9 




6 10 




19 




16 253 




114 




35 




115 




w^JE 




78 




35 




78 




9 




24 231 





next . 



16588 





64 



ino : 



LI" HL, 
Lit HE,. 
INC HL 
LB BC, 
AND ft 
SEC HUBC 
RET Z 
HDD HL, BC 
LD B, IS 
INC DE 
DJHZ inc 
IJKHL>,D 
INC HL 
UKHL>,E 
INC HL 
LD C, <HL) 

INC HL 
LD E, <HL> 
ADD HL.BC 
,TR next 



CD FILE) 



Cornmerrts 

HL=Prc^rarnStar*t -1 
Mew linenumber =6 
HL=address o4 1st byte 

If 

HL-D FILE 

then 

return 

€-lse 

New 1 inenuuber s 

New I i nenumk>er+ 

10: 

Linenumber 

New I i nenumber 

HL= 

HL+ 

Text length 

( lesuina HL set 

to last byte of line) 

next line 



Security numbers 



£N*/ 



A D Robinson, 
Watfr on Degrng; 
South Yorkshire, 

With the popularity of private bank-account 
and home-finance programs for the ZX-81* my 
routine requires the entry of a security number 
before a program will run. Any incorrect entry 
will mean the execution of New s and the 
program will vanish. 

Because the routine is written in machine 
code f il is possible to break out or return to 
Basic without the correct cock which can be 



made up of any dumber of digits in length, 
The first line of the program is a Rem 
statement into which the machine code will be 
Poted The number of Xs in it is determined 
as follows: 10 for each digit of the security 
code plus 2L For exarnpie a three-digit 
security code would need 51 Xs in line ], 
Enter this short program before your main 
program: 

1 REMXXXXXX etc, 

2 LET A = 16514 

3 INPUT 8 

4 POKE A. 3 
5LETA-A + t 
6 GOTO 3 



Now run this, and enter the following 
numbers, pressing newline after each: 
205,187.2,44,32,250,206,187,2,68.77,81,20,40, 
£47,206,139,7,126,201. 

The next few numbers form the machine 
code to check one digit. Entef them as 
required depending on the number of digits in 
your chosen security code, 

205,130,64,254,44,40,3,205,0,0. 

The number underlined is the one you must 
alter to the code of any key you choose — at 
the moment it is set for G. Finally enter 201, 
and then press to halt the program When you 

(continued on next p&geJ 



YOUR COMPUTER. DECEMBER 19&1 71 



(continued from previous p&geJ 

List, you will see ihai the Rem statement now 

contains the machine code, Lines 2 eg 6 can 

now be deleted — their job is done. Now 

enter: 

2 RAND USR 16534 
To make the program Run automatically 
after loadings enter the following at Che end of 
your main program: 

9995 STOP 



SOFTMKE FIVE 



Card Sharp 



f -> 



C J Davison, 

Newton Abbot, Devon. 

My routine, create^ stores and shuffles a 
pack of cards in the normal way. The advan- 
tages of this are that the shuffled array may be 
called in order — Lc, A$(l) to AS(52) — and 
yet the output is complete!}' random. Once 
you have gone through all the cards, you just 
call the shuffle routine, and you are ready to 
go. 

Using this structures Fontoon for instance 
becomes very simple and easy to write since 
the cards do not need to be picked randomly 
and the whole pack can be used. The Basic 
used is Xtal 2.2. However > because or its 
simplicity and size — less than 5K — it should 
work on any system without any alteration. 

Real-time clock 



Kama/ Jabbour, 
Safford, 

HERE IS AN efficient way of realising a 
24-hour, real-time clock for the Acorn Atom 
using its 6522 VIA. Once initialised, the 
program occupies only 130 bytes of machine 
code. Time is permanently displayed in hours* 
minutes and seconds at the top right-hand 
corner of the screen. The clock doe* not 
interfere in any way with ihe operation of the 
system, A programmable alarm facility is also 
provided. 

Among the facilities provided by the 6522 
VIA are two programmable counter timers s 
CTl and CT2. Used in the free-running 
mode, CTl — addresses * BSQ5,6,7 in the 
Atom — creates an interrupt each time the 
count is decremented to zero. Nore mat tLnk 
LK2 on the Atom must be closed for the 
interrupt request of the VIA to reach the 6502 
microprocessor, 

CTl has 16 bits and is decremented at the 
Atom clock rate of 1MH?., so a programmable 
delay of up to 65,536jas. can be generated, In 
our application, CTl is programmed to give 
an interrupt every 50ms. — line I DO in the 
program listing. The recurring interrupts are 
used as the time base for the clock. 

The clock is incremented by one second 



9996 SAVE 'ANIYNAME 
9097 GOTO 2 

Save the whole program by typing Goto 
9996. It will save as normal, but, more 
importantly , when loaded back from tape it 
will run immediately. This means that no-one 
can gain access to the main program without 
the ex Act code. 

The program works by scanning the key- 
board waiting for a key to be depressed. When 



this occurs, a rout me h called in the ROM 
which finds the code of that key. This is then 
compared with the code you have programmed. 
If it is identical t the program jumps to the next 
section to wait for another key depression j but 
if it is different, the program calls the routine 
in ROM which executes New, 

As any ordinary key or shifted key code can 
be selected, even a two-digit security code 
gives more than 6,000 possible combinations. 



■j 

10 
2S 
3& 

48 

50 
60 
70 

>;u 

90 
100 

110 
120 

13a 

140 
15S 



REM *** SET UP STRINGS *$* 

DIM fi$ <53) 

C=6 ■ 5* ="CLLIBS.- HEARTS- SPADES, DlftMONIiS" 

D*= "RCE ..TWO. -THREE FOUR. FIVE. SIX.. SEVEN EIGHT NINE: 

TEN „ JACK. QUEEN KING," 

REM **# CRERTE UNSHUFFLED PACK *++ 

FOR S = 1 TO 4 

FOft N = 1 TO 13 

C=C+1 

H*<C;=HlD*<Df,N*5-4.5> + ,( .0F i ,, +t1IDt-;:&t,5*?»fe>?> 

NEXT H 

HEHT S 

REM *+* SHUFFLE pHCK *** 

FOR C= 53 TO 2 STEP - 1 

rt-IHT':l+52#RND<8)> 

fl*<X> = ft*tfi> s fi*(Fl> = fl# CC-i) 

WENT C 



FULL STOP IS EQUIVALENT TO H SPACE- 



every 20th interrupt — lines 250-260. Time is 
permanently stored at locations # A0-# AS in 
ASCII format* and is copied on to the screen 
at top right- hand corner locations #3017- 
# 80 IF at every interrupt to avoid any flicker 
of the time display during computer operation 
- lines 230-240. " 

Lines 270*360 increment seconds, minutes 
and hours as applicable, and reset the clock to 
zero at 2400 hours. Lines 365-400 compare the 
current time with the alarm setting stored in 
ASCII at locations # AB-# AE, every minute, 
The alarm can be disabled by storing zero in 
location # AF, 

When the pre-&et alarm time is reached, i 
user subroutine at L is called and executed — 
in my program L*#A00O where I have a 
utility EPROM. Lines 210 and 420 preserve 
the registers of the 6502 so that normal 
computer operation is not disturbed by the 
clock routine. 

The Basic part of the program assembles the 
real-time routine and initialises the clock and 
the alarm. Press ESC if no alarm b required. 
After initialisation , only the 130 bytes of 
machine code are needed for the clock 
operation j and the source code can be 
destroyed. 

The machin^codc routine is relocatable by 
changing the value of P — P= # 2800 in this 
listing — and can happily reside in the utility 
EPROM. The alarm setting can be modified 



by changing the contents of * AB^# AE* e.g.: 

J#A8 = - 31373330 

will set [he alarm to 1730 hours. Note that the 
alarm is automat sea \\y disabled once reached. 
It can be enabled by storing a non-zero 
number in # AR 

Once the initialisation routine is ran, the 
Atom can be used as normal, The clock 
routine spends some Wjjs. ae each interrupt to 
update the display. So the operation of the 
computer is slowed by about 0.1 percent only 
— insignificant, and programs rim at normal 
speed. 

The bell, CTRL*G, sounds a bit shaky as it 
is interrupted some 10 times. Obviously, the 
clock stops when loading or saving programs 
as the COS disables interrupts. The displayed 
time could always be updated by modifying 
the contents of »A0-#A7. NJoLe that the 
interrupt is enabled when the Break key is 
pressed, 

Finally, the clock may run slow or fast 
depending on the crystal in individual Atoms. 
This can be cured by changing the contenis of 
# 6805,6,7 - or line 100 - as the 50ms, delay 
is obtained by 

(195)-256 + (801 =50000 

where 195 is che contents of locations # &805 
and # B807 t and 80 is the conients of # Bd06 
for fine adjustment, 



{ 


REM PEAL - TIME CLOCK: F0* TH€ ATOM, BV KRHAL JflMKR* 


186* Pp*21 


13 


DIN £B5.: &0S, *- 005. A 


1 JB P-uttOQ i ^2G4-Pfc£5* ! #2G5 "P/256 i L-ifie^e 


20 


IN, "TIME, HOURS "H- "HI NUTES'TIi "SECONDS "S 


iOTC LEA B+4 


30 


?*H0"Hr , lG+4*,?»fll-H;;iB+48, Ptft2*#3fl# Ht9F«32 


^10 ^T^f\f, $TV»flA 


40 


?t*fl3 -M/ 1 e+43 ; ? BfW-rt^ j 0+43 : ? #R5 -#£6 


230 LE^S 


50 


^#A6- 3 / 1 0*4 8 ■ ?M ? «SZ 1 0+46 . ? # AS-2G 


24S B£2 LDA#9F,X, Sm^ei?,K,D£K;fPL BB? 


60 


■ j #AF-e 


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2«e LDRaa&. $tmh& 


tie 


IN. "ALAPtl HCiUft^"H, "MINUTES "M 


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2^6 iHCtfl?* GPm&i BHE BB3- ^TA*A7 


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29^ INCiAo- CPVUA^. l^E BBS- *TA*Ae 


14* 


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K»Ci rnc*fl^, CPV:#fl4, BNE BB4, ITMM 






(fisting continued on ntxt page/ 



72 YOUR COMPUTE*, DECEMBER t981 



SOFTWARE FILS 



(listing continued from previous page) 

32^ IfCflftl, CFXtfli, BE& BBS 

33B LGKf#34; CPKItil; BNE B£4 

34& LDtfM3fr CFX#flu, Eh£ £B4 

350 LD^*2f ■ $TX#Aia 

36*- £E5 STRttfll; INC#R0 



j(S0 LDfl*Fi3, CWPdflC, BHE BBS 

_^li LBtWftl- CMPtflU; BNE EBo- 

406 LDfitWe, CMP#flE, SHE FB3 

4Ki LLI. LDflaQ,STfl*fiF, J*F L 

4£& £B3 LE\#A&; L&V#RRh PLR, 

44u F.**.R. 



RTI 



Demon at the wheel 



Richard Bassett, 

Sutton Cofdffefd, 

West Midlands. 

Demon iikivek will run on a Sharp MZ-60K 



im^m 



and uses approximately 2K. The idea of the 
game is to destroy as many people as possible 
without hitting any of the white barriers. The 
car moves across the screen and the key "B" 
will move it upwards and l| M" downwards: 
"N" holds the car straight. 
In a tight spot, the £ key will destroy all 



barriers and people in sight, The "V" key 
produces a machine-gun effect which can be 
used five times, After thisj no firepower is 
produced until reloaded. Whenever you hit a 
person m harrier, a certain sound is produced. 
As well as the maximum number of people 
destroyed j the time is also given. 



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PRIWT-I 1 - ittTtJW 

IF LC:-2 TKN 5W 



Sound-box 



^r-jv 



J Ch&imsrs, 

East Grin&teod, West Sussex, 

Have YOU ever wished that your ZX*8t 

could play tunes, give audible warnings, add 

sound effects to games or just make noises? 

Sound b made up of a series of clicks in rapid 

succession. If the ZX-81 can produce these 

clicks rapidly enough, the noise produced 



CMOOnF Wire link 




Dirpct*qn of tracks 



trtVITHWf 

iCw>ckit 
TriAClGB 



C^I*etor 
JCl MLS 136 



! StripboAnj component Igyout 



represents a musical tone. The more clicks per 
second produced^ the higher the note. 

To achieve a sufficiently tast speedy the 
sound box can be used only when the machine 
is in Fast mode, Again, for speed but also 
because of the limits or the tiaaic language, it is 
necessary to use a machine-code routine to 
produce the noise required. The note required 
is selected by Poke commands. 

Poke 16536 will vary the frequency of The 
note and very fine tuning can be achieved. 
This Poke will from now be known as the fine- 



tune byte. Poke 16527 will vary the base 
frequency j and will be referred to as the 
coajse-tuning byte, The length of &he note b 
5*1 by Poke 16519, and ihis will be known as 
the length byte. 

The circuit can be constructed on a piece of 
1 ()*by 1 0*hole J in. sEripboard. U the diagram 
is followed} construction should be simple. 
Only eight connections are needed to the 
computer and they can either be hard- wired, 
or taken to a 23-by-23-way edge connector 
plugged into the expansion port at (he rear. 
The sound output is taken lo a small 8-ohm 
loudspeaker. If a greater volume ia required, 
rh& speaker ean be disconnected and the 
output taken io a suitable amplifier. 

The chip used in the circuit is a thrce-to* 
eight -line decoder. The three lines are the 
lowest three bits of the address bus 3 A0 S Al* 
and A2, If the chip is enabled using ail three 
enables lines pro vided and t hese lines are 
connected to A4 3 IORQ s and WR, it is pos- 
sible to produce eighi port-select lines for 
ports 8 io J 5. By trial and error H was found 
that port 1 1 was not actually used by the ZX- 
81. This port-select output can, therefore^ be 
used to make the speaker click every time the 
port is written to by the Z-80 Oui(C), C 
instruction. This is where the machine code is 
required. 

All you have to do is to write a short routine 
to call port 11, wail depending on the note 
rcquiredj and then jump back to calling the 
port. To make a note of certain length and 
then return to Basic is achieved by encasing 
the routine in another loop which returns to 



Basic after completing a number of cycles. 
Listed here is a Basic program which 
enables the machine-code routine to be entered 
into the memory, Also listed here is a he* 
dump. After the Basic program has been 
started s you enter this hex code, two characters 




at a time with a press of NewLine between each 
pair. 

%'hen you have typed in the code a 9 error 
report will appear at the bottom of the screen; 
try entering Run 100. If you have done every- 
thing correctly your sound-box should be 
making a series of random notes. 

When you have built your sound-box and 
made it work, you can start writing software to 
control it. Any program which is to use the 
sound-box must contain a Rem statement in 
the firsi line. This statement will contain the 
machiiie-cude routine. It b advisable, there- 
fore, to add lines to the program. Alterna- 
tively, the lines can all be deleted, with the 
exception of the Rem statement. 

As 1 mentioned, there ate three controls to 

produce a sound, these arc coarse, fine tune, 

(cQntinued Oft p#&e 75} 



YOUR COMPUTER. DECEM&ER 1981 73 



±J0^ for all 
^^ACORN ATOM 

owners 

PROGRAMMER'S TOOLBOX 

A pecked 4K EPRQM (fits Utility Socket) containing; 
1200 8AUD CASSETTE OPERATING SYSTEM 
Visible Load Routine 






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nascom magazine 

■ Micro power" 



Series anictes. club news, toners & answers* Packed full of useful 
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s ALL ATAftl $4ITwAMf NK tJliLCSS S f ATtO 



74 YOUR COMPUTER, DECEMBER 1981 



SOFTWARE FILE 



(continued from page 73J 
and length. For normal musical sounds ic is 
advised to leave coarse tune set at 2. Poking 
Fine tune with will produce the highest note 
availably and with 255 will produce The 
lowest note, Poking length with will deliver 
(he longest note available and 255 will deliver 
The shortest note. 

When the various controls have been set, the 
following line will actually make the noise: 
LET SOUND = USR16514 

To ic$i the controls, use the same program 
as before and type Run 200, You will be 
invited to type in a number between and 255 
corresponding to ihe length of note requiredj 
and then invited to enter another correspond- 
ing to the frequency of the note required, It 
will then play the note. 

Maths teaching 



HEX DUMF 

0£ OB 3E 60 16 00 14 RR GS 

ED 49 21 FF ©2 BC Cfl S3 40 

2B C3 SF 40 S 



BASIC FRQ"3RflH 



1 RE hKXK XX :-::-:: <>®ocxXK)0&dOd$0O< 

2 LETX-0 
19 INPUTftf 
2© PRlHtftS; 

30 IFft*="S"THEMCOTiifli3 

4l* LETB=lG#CODEfl*+COOBF**<2;>-476 

3G FGKE165X4 + ^:.P 



79 GOTO 1 a 

30 FR J NT "TOP" 

90 STOP 

100 FFliT 

lid POKE 16513, INT CRMD*255:> 

1 2 O POKE 1 «S24 , I NT < RN D * 2 5? " ' 

130 LETS0IJHD=USftl6^14 

140 GOTO 116 

£00 FAST 

210 PRIHT"L£HGTH?' - 

220 IHPUTL 

230 P0KEL£5l9^L 

240 PRINT "NOTE?" 

2^10 I NPUTL 

2€G P0KEie526,L 

2 ?Q L E r SOUND =USR 16514 

2:_-U iVl. 1 l>I' 1 O 



S£M2? 



W /V ScBrfett, 
Maidenhead, Berkshire. 
The IDEA FOR this program originated from 
the Mathematics program Lrt the Sine! air 
software catalogue* but it is a considerable 
improvement — particularly in ihe way the 
program seems friendly to the user. The user 
begins by entering his name which appears 
during the program run and the computer 
acknowledges by printing "Hello, I am the 
ZX*S1" on the screen. 

The function required, +— % is entered 
directly, rather than via a numeric code and 
then the user is asked by name for [he level of 
difficulty he requires. Levels 1, 2 and 3 are 
offered on the screen but any numeric value 



can be inputted, 1, 2 and I produce sums 
capable of solution by mental arithmetic. 

Lines 130 and 140 derive the two variables 
used in the question, "C 1 is related to |l D" so 
that a negaiive result cannot be produced and 
in division the answer will always be a whole 
number. Line 150 assembles the sum into a 
string which is printed on the screen together 
with " = ". This string consists of the variable 
"D Ti with the operator entered earlier, and the 
variable "C'\ 

If the answer entered in response to printing 
the sum on the screen is correct, jhe score 
variable "5" is incremented and the user is 
told by name that his answer is correct and the 
score out of the number of sums attempted so 
far is printed . After a delay, the screen clears 
and a new sum is presented. 

If the answer is wrong, "Wrong" appears on 



the screen and the sum is reprinted with the 
correct answer. For extra impact, "Wrong" 
can be programmed in reverse characters. 

After 10 sunns have been attempted, the user 
is told "Well done 11 , and his score out of 10 is 
printed. This display remains on the screen 
for several seconds after which the program 
restarts automatically. 

The Pause function has not been used 
within the main body of the program where 
delays were required since it tends io cause 
disturbances to the display. Instead, the single- 
line X = RNO**HND**RND 
is used, A Fcr-N*xi loop could have been 
used, but it would have required two lines for 
each delay. The program will run on a IK 
ZX-61 and should provide i good deal of 
educational entertainment for the younger 
members of the family. 



5 REM "SUMS 11 


160 


PRINT B*; n ="; 


10 PRINT "WHAT IS YOU NAME?" 


170 


INPUT D 


20 INPUT US 


180 


PRINT L 


30 PRINT "HELLO ";Nf J "> ", , "I RK THE ZX8l" 


190 


IF ABS <VAL B* -H»0.01 THEN GOTO 230 


40 LET X«RNIi**RND**RND 


200 


LET S=S+1 


60 CL5 


I'ijt" 


PRINT ,, "CORRECT, " J N*;V" 


70 PRINT "DO YOU WANT + - * OR / ?" 


206 


IF N=10 THEN GOTO 280 


30 INPUT fl* 


210 


PRINT S;" OUT OF " f Hi" SO FAR. 1 ' 


3Q PRINT "HON DIFFICULT, " , Ut; ".. ■■„ - 1,2 OP 3^" 


220 


GOTO 240 


100 INPUT B 


£30 


PRINT ,j "WRONG", B*; "- 11 ; VflL B* 


105 LET S"0 


240 


LET X=RND**RND 


110 fOR'N=l TO 19 


260 


NEXT N 


120 CLS 


25* 


PRINT "WELL DONE," >> "SCORE"; 8;" OUT OF 10." 


130 LET C=1 + INT<:5**B*RND) 


300 


PAUSE 300 


14@ LET D=C*INT<5**B*RND> 


310 


CLS 


150 LET B**STR* D +R*+STR$ C 


320 


RUN 



Zero dropper 



mm 



G Stephen, 
Aberdeen. 

The FLOATiNG^point ROM in the Acorn 
A*om is very untidy when ic come* to printing 
floating-point numbers on the VDtl The 
display take* the form 3 ,70000000 for the 
number 17 and the form 6.2BO000O0E-12 for 
ihe number 6.2S*I0 _ \ It would be much 
neater and more easily read if all the trailing 
zeros of the mantissa were dropped, and that is 
the job of this short subroutine. 

The floating-point number to be printed is 
held in the variable ZN and the subroutine is 
called. The first line after the Rems — line 
10010 — converts the number ZN to a string 
and stores it in the free RAM space starting at 
location 540 decimal. 

If we assume that the number held in ZN is 



540 



6.230Q0CO0E— 12, the string format will be; 
2 8 f - 1 2 1 JJ 
560 554 

There are two specific string areas used for 
this conversion^ the main area is 540-554 
decimal which holds the mantissa* and the 
secondary area 560-564 decimal holds the 
exponent, 

Line 100 10 also sets the secondary string to 

the null string by storing 13 ai 560, The 

carriage return character 13 also signifies the 

end of a string. If there is an exponent, line 

10030 is activated and proceeds to separate the 

mantissa from the exponent by moving the 

five bytes of data from 550-554 to 560-564. 

Then it siores 13 in 550 and so terminates the 

mantissa string, 

6-28Q000QDE-1213 

1 I 

560->E - 1 2 13 

6 = 2800000013^550 



We now have two strings 5540 and $560 — 
$540-6.28000000 and £560 -E- 12 - so we 
can proceed to remove those zeros in S540. 
Line 10050 does this by substituting the string 
terminator 13 for every zero until a non-zero 
value is detected. 

Line 1 0060 then removes the decimal point 
if appropriate and the next line prints the two 
strings before returning to the main program. 
The value in ZN remains unchanged and can 
be used in further computations. This routine 
can be saved on tape and appended on to any 
program requiring a numerical printout. Here 
is a table of ASCII characters and their 
decimal values used; 

ASCII Decimal 

carriage return 13 

46 
48 

E 69 

(continued on peg& 77f 



YOUR COM PUTE R , DEC EMB ER 196 1 75 





memory 





The M EMOTECH memory extension board will allow 

theZX81 to run 48 K BASIC programs which may 

include up to 16K of assembly code, 

The unit contains a genuine 48K of user transparent 

RAM , and accepts such BASIC commands as: 

10DIMA(9000). 

A range of I/O Port boards and AID, Of A converters is 

available. The unit is compatible with theZX Printer, 

and RS232 interface will be available soon. 

The MEMOTECH memory has a fully buffered control- 

data^address bus with PCB 40 way header plug< 

The ZX81 sits on a custom built case which contains 

:ne MEMOTECH memory and a power supply which 

not only powers the MEMOTECH memory, but also the 

ZX81. 

AH Leads are provided. The MEMOTECH memory 

extension board costs: £109.00 + VAT in kit form, 

£129.00 + VAT assembled, 15% Educational userdis^ 

counts are available. 




Please make cheques payable to: 



nenoTecH 



(Sales Dept.) 103, Walton Street, Oxford. OX2 6EB, 



SOFTWARE FILE 



/continued from page 75) 


?i0440 1*149 


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&&mm *c* w/w «m«A(w>p mis f*£E mk s^flcc ft##^M#rN«i 


>/#f«* jf ?/*« r«w ?j*jj 


>/»/# 5 7 J? t* r 3#* r >56#*/J 


> 10070 PRIMT iVf^M* ' 


> 10020 if ^3*r>4* r«H flffTO 100*0 


>JH«ff flf TtfijW 


>1M30 f&R J -34* TO J3* f 1?10*'>I j HIX7 1 t 735*M-JJ 


MIMf 



Never a crossword 



£?=®7 



te/b Hancock, 
Potters Bar, 
Hertfordshire* 

This program, written for a ZX-81 — or a 
ZX^SO with i he 8K Basic ROM — will print 

on the screen 20 anagrams of a word input by 



the user. The main ski ion of the program, 
lines 1 30- 180 j removes a leutr from the word, 
displays it and updates the original string, 
It then repeats this until there are no more 



letters and returns to the beginning. The 
maximum length of a word on an unexpended 
ZX-81 is about 10 letters, so a RAM pack 
would be useful. 



m*®) 



Half life 

fteymond Nugent ¥ 
Aberdeen r 

Half life nay be of interest to science 
teachers. It was developed using the ZX-81 
with 16K RAM. The program simulates the 
radioactive decay of a sample of 196 radio- 
active atoms which decay exponentially with 
respect to time. 

The display shows the 1 96 atoms decaying 
randomly within a square and there is a 
continuous tally of the numbers of atom* 
which remain undetayed and those which 
have decayed as time passes. The display also 
gives an activity /time graph and the half life on 
two separate occasions. 



5 


REM *RNflGRflRS BV 1. HANCOCK* 


lie 


LET A«LEN fif 






I-U 


FOP %=i TO ft 


10 


RRHD 


130 


LET C=INT vRND*ft)-+l 


20 


PRINT AT 6, 11; "ANAGRAMS" 


140 


PRINT AS CO; 


3@ 


SCROLL 


ISO 


LET tP*=ft* (1 TO C~l> 


40 


PRINT "PHRASE?" 


I60 


LET Ef-MCC+1 TO> 


58 


INPUT Et 


17£ 


LET fif^Df +E* 


Co 


ill 


136 


LET A=ft-1 


?9 


PRINT TAB 10; "PHRASE-* ;B* 


ISO 


NEXT 6 


SO 


PRINT 


260 


PRINT 


9** 


FOP 1"=1 TO 26 


110 


NEXT B 


\m 


LET A*=B* 


: id 


END 



Line 10 Sett up Dim space for 196 atoms* 
Variables X and Y give the number of decayed 
and undecayed atoms respectively. The 
variable E stands for the total number of 
attempts which the computer makes at finding 
an undecayed atom — this is equivalent to 
total lime. "V* 1 is used to give the correct 
number of "— t+ in subroutine 400- 



"I" and "J M are selected randomly - if 
A5(IJ) is null [hen the display shows a pixel 
unplotted simulating the decay of that 
particular atom. A$(I J) is then made equal to 
one and the tally altered. If AS(IJ) is not null* 
there is no change except in the time tally. A 
pixel showing the number of undecayed atoms 
is plotted every 14 attempts. 



5 


REM "HALF LIFE" 






222 


PRINT ftT 4,8;" DECAYED : "iffT 6,8; '■JNDECflYED" 


10 


DIM ft*<H, 14' 






;;:?■ 


PRINT AT 20,28; "TIME" 


15 


LET E * 3 






223 


PRINT AT O^^flCTIVITV" 


29 


LET V = 196 






230 


FOR R = 1 TO 14 


30 


LET X = 






232 


PRINT RT 8, 22 + jt/'1.6J¥ AT 8, 22+R/l , 6 J *H" 


43 


LET V = 






234 


PRINT AT R/2,23;'1T ; AT R^S,31, W 


5© 


GO&UE 198 






240 


FOP H = 1 TO 14 


^ 


FOP H = 1 TO 14 






258 


PLOT 47+R,27+H 


60 


LET E - E + 1 






255 


NEXT H 


65 


LET r ■= UNTvRNri*14>+l> 




26& 


NEXT R 


70 


LET J = aHTiPNH+14 ■ 


+ 1 ■ 




265 


SLOW 


30 


IF ft*<T,J>- u " THEN 


&QSUB 


5&9 


26t= 


PAUSE 180 


90 


PRINT AT 4. 19; X, AT £ 


> 19;V, 


"1 IT 


270 


FETMRN 


91 


PRINT RT 3,28; E 






400 


FOR W= 1 TO (V/2)-l 


92 


IF V - 93 THEN GQSUB 


400 




418 


IF V >• 98 THEH PRINT AT 12, HJ "-'SRT 20, <V/2>-l,E 


93 


IF V - 49 THEN 6CSUB 


400 




420 


NEXT W 


95 


IF N - 14 THEN PLOT 


W-ltClNTWti))* 


430 


RETURN 


180 


NEXT N 






500 


UNFL0T 1+47, J+ 27 


101 


LET V = V + 1 






510 


PLOT I+47,J+27 


ne 


GOTO 55 






520 


UNPLOT 1+47, J+27 


190 


FAST 






530 


LET K-K + 1 


200 


FOR % ~ TO 63 






540 


LET V=V -1 


21© 


PLOT £,0 






558 


LET fl$<I,J> = "1" 


il 5 


PLOT 0,0.6?#B 






560 


RETURN 


228 


NEXT f 











Palindromes 



m»W 



Tim Goldmgham, 
Maidenhead, Berkshire. 

Sex at noon taxes Apart from its biological 
significance* this observation by John Julius 
Norwich is interesting because if is a 
palindrome — that is, it reads the same 
backwards as forwards. 

Palindromes have always fascinated literary 
men, In a Charles Osbourne's recent 



biography of W H Auden, The Life of a Poet, 
the following is quoted: 

T Eliot, lop bard, notes putrid tang emanating, is 
sad t [ H d assign it a name; gnas din upset on drab 
pot icilei; 

This has S5 letters; but according to the 
Guinness Book of Records the longesi 
palindrome, devised by Jeff Grant of New 
Zealand, has 11J25 words. 

You may not be able to match that record, 
but you can have some fun with this ZX-81 
programj which displays text both fo wards 



and backwards on the screen as you type, thus; 

SS 

SEES 

SEX XES 

SEX AAXES 

SEX AT TAXES 

SEX AT NN TAXES 

SEX AT IVOON TAXES 
Because the program uses tnkeyS, the space 
key would be interpreted as Break, so the 
adjacem key is used for spacing: a fuJI stop 

f continued on next page/ 



VOUn COMPUTER. DECEMBER 1901 77 



^continued from prevfous page) 

gives a space on the left, and a comma on [he 

right: **i shifted H, clears [he screen ready for 



SOFTWARE FILE 






you to iry and create more new palindromes. 

As an extra refinement;, if the palindrome 

pivots about a sin pie letter as in the Auden 



example, a single * will remove the duplicate. 
The Rubout key can be used in the normal 
way. 



1 REM PALINDROME GENERATOR 


180 LET fi$=A*<T0 LEN A$-l> 




110 LET B$=B$<:2 TO LEN £*> 


2 COPYRIGHT T P GOLD INGHAM 1331 


120 GOTO 190 


10 CLS 


130 IF «<>%" AND C*<> M i" THEN GOTO 170 


20 LET R*="" 


148 IF C*- ,, . M THEN LET Ft$*ft$+ U & a 


30 LET B*="" 


ISO IF C$«%" THEN LET B$=W+B* 


48 PAUSE 40008 


169 GOTO 190 


59 POKE 16437,255 


170 LET fl$=A*+C* 


60 LET C$=INKEY$ 


138 LET B$=C*+B* 


70 IF C*="** M THEN RUN 


190 PRINT AT 10,0;" 32 seaoes 


30 IF C$=°*" THEN GOTO 110 


208 PRINT AT 18,0;*$,** 


98 IF CtOCHfi* 119 THEN GOTO 130 


218 GOTO 40 



Paying a mortgage 



KWsrd, 
Nottingham. 

My wife and I had decided to move house, 
but w€ did no* know how much this would 
cost in new mortgage repayments or how 
much we could loan from a building society. 
After enquirieSj we found as a genera] rule thai 
a first-time buyer could usually loan between 
two and two-and-a-half times his annual salary Y 
and if you are on your second or third house 



you could loan only two lo two-and-a-quarter 
times your annual salary, if loaned over about 
20 years. 

The next problem was to calculate what the 
monthly payments would be before and after 
taa relief All this is done by our program 
which is written m Bask and on a l&K Pet 
2001 series with the large keyboard. The 
whole program consumes 1^835 byres of 
memory but there are many Rem statements. 
Also the line statements are kept short to make 
it easier to understand. 

The reverse character "R" prints the 



statement in reverse characters, The reverse 
character M S" homes the cursor. The Tab () 
starts printing after the number of spaces 
indicated in the brackets — a maximum of 255 
is allowed on the Pet. 

iNTfPNxTOO + .SI/lOQ 

rounds up id the nearest two decimal places, 
Line 200. A change in the For-Next loop in 
tine 200 will alter the number of years 
displayed on the screen: 12 are shown on the 
Pet. Any more and information will scroll off 
the top of the screen. 






FFJNT 
■ X PFJNT 
IF £0 Att$U&%-V Ctf'H- 



15 Kfl--!-»euftS€fi I* 

Eft ren-CHRPM+r^CLBW SCfiN.+CURSE* HM 

is P£i*-T*Tfc<-r: •!"**>.■ as 8Ec:r*L 

:e fl£rr-[-[«TEJfKr-JippiOMTptv jhiep£St 

33 *£lt-*-5AUMty 

4* PfitHTClAf f]4?> 

4* FfMHTTAmCO " #K*tC«0£ FECOEW 

14 HtfjT-UHtf JS W* HHUft. 3flL.*V 

T3 IMFUT" Aft* VflU * FIfi$T TtKE IUVEF? IF 80 A«5fc€R'V C*'H u . ft* « MT 

tffl IFN* a »H i 'lME>tf h 5 

« fff|llT-fl$ A FJftST f(/* BWQ? VW *t 0$4JfiL¥ "LOUP i,5 TJHES VGU* " 

"tf P* 1-lTTA^^l -T IfrMtfL StfLflftV ,im> :- JIT. .'. t .. > ■: IrJ GOTQS^ 

r» miimt*-a* v» «e hot ft f i«t ri«t JOTS* «u a** uauftjv cmlt alow* " 

$* W|HrT«t«>*T3 r«» T[HES yft* *#M4L MLB* IMKH If --J|-2.:3*5; P*)NT 
SS iFtfUT "IMAt J} M 313 OF Ti€ LC**i T .fV PffDif 
M MPL'T"l«ftf IS STMOOTD RflT£ <?F fife - f FPlFlT 
JS INPUT"***! !£ TrC TOffTWGE Hit. P^TC M I PR[lit 

IM IhFWaGW Jtf*JY V*WS H T^ Ltift* FCft" tl HUNT 

l:o []•■ i.'iwj 12 ni«mi£ *en ii^flONncv irfift$ j^cr#L-^J*i^-^ tOtfTK ?■» l**i 

tJS ^-PV4H RChf IMTCPE^T C'N L'>.«- 



19 PtM~{l*ll>r-III 

139 miNr"W LO** Gri*F'.'-Cvff'-PrvE«S- 
14« f»EKT*!HE N0HTIH.V FftVf«'iT3 WT4* J*. 



:ss 
in 

!=* 
..V 

:n 
as 
:i- 



jfr:;rirf:wv.; im 



FPiWT-*J|tn Tft IPCLIET WJTHLV PftWClftS ȣ * 

T3-iatTJ PgPI TftX SELtEF 

S-T>tfi'i«JNT<S*l£W*.5^.'I« P^?T TflK RtL. 

W-S Pl'\ TO- jfiVJN&S 

P-s»FM-^P^-<:,-|Wim>,-li -Rtlt PfiWCHTS hFT£* 7^ j P£l, 

FS»lH7fW*lW*.3- ■:« 

r^FVtJi-FN+i; RBt LOrtN ftFTEP AHN. FflvnEir 

IFIClJlHEHFHJfrt-|frEftFV.-S» , F$."L««M L£FT n [MT^PVH»**! 

hc-;t J 

Ft [PIT FP[KT'THC TIThL 
fft|MT*T ASSURI.'U A T 
F*|OTTlUi»t~***lHT' Alt | ft»».3 ),--!» 



rtWXM" prtj[i C"VEP"*ft*-i43'trvef*^ 
ri ; th f i ■ ■ * i oil) * . T » . J 00 
:: RELIEF TF-T-r: 



.■i: 



JW 



-if toputff Ffiic :^ 



Transposing music 



33^3/ 



J f W/Jcenr, 
Reading, Berkshire. 

Tuts program was developed to transpose 
music from one key to another. The string AS 
contains the 12 notes of the chromatic scale — 
■he flattened notes arc represented fay inverse 
characters* 

The rest of the program converts the notes 
input in string BS to integers or near- integers, 
then adds T, which is the number of semi- 
tones through which you want to transpose the 
music, and reads the appropriate note from 

\i 

Obviously, if you wane to transpose down 
you either use (12-T) o* change the plus sign 
in line 1 10 to a minus symbol. The program 
has been simplified in line 310 which will not 
return an integer — as you can see if you put 
line 1 30 to 

PRINT P; AMP) 

Yet the number is treated as the next highest 
integer — this saves some space- Some 
interesting patterns can be generated by this 



5 


REN " TRANSPOSITION " 


10 


DIM m* '12) 


20 


LET R* = N @iiECir@EFQ& h| 


30 


LET T = ?? <the number of semitones o* transposition) 


40 


INPUT B$ 


50 


FOR N - 1 TO LEN B* 


60 


LET P = CODE B*<N) 


70 


IF P>45 THEN GOTO 300 


80 


LET P * & - 3?>*2 


?c- 


IF P = 6 OR P = 8 OR P = 10 THEN LET P = P - i 


100 


IF P> 10 THEN LET P = P - 2 


110 


LET P - P + T 


120 


IF PM2 THEN LET P = P - 12 


130 


PRINT A*tP>. 


140 


NEXT N 


150 


PRINT 


160 


RUN 


300 


LET P = P - 165 


310 


IF P>= 2 THEN LET P = P + P/2 


320 


GOTO 110 



program. For instance! put T = 5, enter BS as 

"CDEFGABCDEF6AB" 
then enter the result which the program prints 
out. Do this until your fust BS is repeated. 
The program can also be used to compose 



music — albeit music of a rather modem 
nature — if T is replaced by a random 
function. For example, delete line 50 and 
change II to 

LETP-P + INTiRND*10) 



78 YOUR COMPUTER, DECEMBER 1981 



Bomb disposal 

Roger Brooks, 



SOFTWARE FILE 



m*m 



Btnton Gfeen, 
Warwickshire r 
THE ARTICLE on games applications for the 
ZX-80/81 in the August/September issue by 
Tim Kartnell prompted me to write this 
program which only just tils into IK, The 
program maps the top left-hand comer of the 
screen with a 10-by-lO matrix. In it lies a point 
which corresponds to the location of a bomb. 
By eniering various points in the normal co- 
ordinate fashion, values are printed which give 
an indication to where it is. 

Obviously* a large number of values will 
lead to easy location and so the score is 
weighted accordingly and printed after the 
bomb has been diffused . 

Those with 16K RAM packs can modify 
thb program to include more elaborate Print 
statement* and a combination problem to be 
solved before the bomb is diffused. 

One tip 1 find useful when programming is 
the use of keywords in print statements. They 
save the valuable memory space in the ZX-81 . 

The words above the keys can be entered by 
the K cursor mode then editing, placing words 
if necessary in front. Those words in red can 
b* entered by simply pressing shift, and it is 
this which must be used in line 19 — the word 
stop. In the list inverse characters are 
underlined. 

Screen artist 

T M Humphries, 

Sutton Cofdfie/d, 

WesrMidfends* 

Page 121 of the ZX-81 manual lists a program 

which draws a Lint; tram pixd (A,H) to pixel 
(QD) but its 25 lines take nearly IK of 
memory $0 it is little use as a subroutine for 
unexpanded machineS- 

My eight-line program does not only the 
same jobj but leaves [he initial values A f B 3 C 
and D unaltered and uses only four new 
variables. As this listing is intended as a 
subroutine you will first need to Input (A,B) 
and (C,D). 

The program works on the principle that the 
distance between the *V N co-ordinates^ X 3 and 
the u y* co-ordinates j Y, can be covered in M 
steps where M is the greater of the absolute 



m>m 



1 FOR X=9 TO 9 

2 PRINT AT li,K;X 

3 PRINT AT X,ll;X 

4 FOR V=0 TO $ 

5 PRINT RT XA'J'L" 

6 NEXT V 

7 NEXT X 

S LET fi=INT<RND#3> 

9 LET E=IHKRND*9> 

li3 LET b=4fi 

11 PRINT FIT 13,9; "DETONATION IN "JO;" CVCLES 

12 LET G=G-1 

13 IF G=G THEN GOTO 22 

14 INPUT C 

15 INPUT D 

16 IF C=R AND D=B THEN GOTO 13 

17 PRINT RT D,C;(INT<<flES<D-B>+RBS(C-fl>)/2> 

18 GOTO 11 

19 PRINT RT 17, 0; "STOP DETONflT ION-PRESS D" 
£0 IF INKEV*="L" THEN GOTO 25 

21 GOTO 29 

22 CLS 

23 PRINT "BOOM" 

24 STOP 

25 PRINT "BOMB SAFE - SC0RE=SG**2 
READY 



1 @08 


LET X = 


c . 


- fl 










1010 


LET V = 


H ■ 


- B 










1020 


LET M = 


fiBS 


3 X 










1038 


IF FIBS 


V > 


M THEN LET 


M 




BBS V 


1048 


FOR N = 


" 


ro m 


- i 








1050 


PLOT fl 


+ N 




/ M, B 


+ 


N 


* V / M 


1060 


NEKT N 














1078 


RETURN 















values of X and Y. The distance to be travelled 
in each step is, there Tore, X/M and Y/M 

respectively. 



The appearance of very steep or very 
shallow lines can be improved by adding Siep 
2 to line 1040 and plotting every other point. 



Ark Royal 

D Ewan, 
Haddington, 
East Lothian. 



22*33 



You are challenged to land an aeroplane 
on the aircraft carrier, Ark Royal There is an 
obstruction at the start of the flight deck *hich 
you must not hit with the wheel of your 
aircraft — landing too hard on the flight deck 
aI$o spells disjii-u:. 



Once mastered^ the game can be made much 
harder by changing line 300, You now have to 
judge your height above the (light deck If it is 
not correct, you will require to increase 
altitude to correct your descent rate. The 
program runs in 1 K. 



14 


WT-C-p-J 




219 


IF FY - IS V*D A - S THIS GOTO 4fflJ 




2fl 


LEt FTf - IBfa {RSD * lj> * 1 




22* 


IF FY > - 19 THEH G0I0 4 20 




3fl 


FOB q * 5 tg ■'? 




m 


If tMKEY* - N 6 4h THEM LET FY - FY * 1 




M 


FOfe A * TO 2$ ST1£? 2 




ne 


IF TNXEYf - "7" THEM LET PY - PY - 1 




i00 
IM 


CLS 

nam at ib, s * *i »i*j at 19. &s "hi 1 ) 

T 1 r 1 ^M\ ''■ ■ ■- in A - 


_^_- M 


3:a 
33* 
^* 

ill 


NEXT A 
NEXT Q 

fRlST AT fl t 1; "LAffiJED", ^i H ATTEMPTS" 

STOP 

PRINT AT Up If "CRASHED" 




[ | mm M - AT i(, 0, ----- ™-™---™ 

fsiptt at 20, 5; -m m m m m m m w 




130 


LET S - £ - 1 






141 


IF S - 27 THEM LET £ * 




*J* 


not 




|$f 


PRINT AT PY* A* Hl || y 1 y» M ; AT FY ♦ *, 


A r 2l "Q" 


m a 


MfJk" ADVANCED GAME CHANCE LISE 3B2S AS Fm,LOWS;- 




240- 


IF FY * 1 * IS AMD A « 3 - £ THEM WID U2U 




-v\< 


IF t^KEY* * 'V TUES t£T FY * Bf # 2 


m 



YOUR COMPUTER, DECEMBER 19@f 7ft 



PUT YOUR 
-_ MICRO 

r&To 

ksWORK! 




YOUR 
MACHINE 




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Tel: 01-6SO 0267 (24 hours a day — 7 days b week) 



00 YOUR COMPUTER. DECEMBER 19B1 



COMPETITION CORNER 



Christmas competition 



BY ANTHONY ROBERTS 
Round 1 

1. When was the transistor invented? 

2 r The Millionaire was one of the first 
calculators sold commercially; when did it 
appear? 

3 Eabbagc never succeeded in making his 
Analytical Engine work. IBM made The 
first machine to uae all of Babbage 1 * 
principles — when? 

4. The first commerical computer was the 
Ferrsmti Mark 1 Star made at Manchester 
University, It consumed 27*000 kilowatts 
of power and had 4 s 00O valves, When was 
It announced? 

5. The first digital calculator machine — ii 

could add T subtract, multiply and divide — 
was invented in 1642. By whom? 

6. One of the first electronic digital 
computers weighed in at 30 tons with 
18,000 vacuum tubes and was called Eniac. 
What did the name stand for? 

Round 2 

What arc rhe names of the frcven Dwarfs? 

Round 3 

What follows in these sequences? 
L 5 12 21 32 45 „> 

2. 8 5 49 1 7 6 10, „ 

4. 1982 1988 1993 1999 2010... 

5. 5 14 30 55 .* 

Round 4 

Flowchart Puzzle 

You are asked to help son out a micro 
evaluation kit which comprises four machines 
— hm y Bat> Cat, Dog — each of which has a 



terminal and its very own connecting cable. 

Naturally 3 everything h colour-coded. The 
wires are coloured ebony , fawn, gold arid 
hazel; the screens are indigo, jade, kingfisher 
and lilac and the machines are mauve, navy 
blue, ochre and puct, 

They have all been packed in a single, large 
box with computer-type instruction* provided 
to enable one to set them up in a straight row 
with each screen sitting on its micro, ready to 
run. But the kingfisher screen is not 
mentioned. Can you say what colour machine 
it connects with? Here arc the instructions 
provided. 




Competition reports 



Thank you for sending in so many entries to the 
October ZX-81 Crossword competition. The winner 

is Gct>rgc Lun£, Lontpinc School Road, Rornaey, 
Hampshire, who LrtnipLeicd rhe sentence, "I will nrn 
use a 2X*81 to run a power station but be less 
'ampercd learning what's Wau in the computer 
age 1 '. A ZX-fll is on lu way, 

Almost everyone etse followed a similar theme. A 
special mention though to J Duncan from Durham 



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for writing M but I did se« the manner of Winds-cak 
in W H Smith". 

Many readers complained that the first puzzle wc 
ran in Competition Corner was mo easy. In 
November we really got our own bafk with Crater 
Robots. Out of all the entries not one of you found 
the right solution — it was hard, rhough. 

We have a saltation, on the Sharp M2-50K, which 
fits into about 2K, of memory and Took abnui nine 
minuies ro fun. It should be possible to write a 
solution to fit into a IK Sinclair, 

There are exactly 7,529,536,000,000 different 
ways for the robots w rnovi, 101 T 56G of which 
produce results in which no two groups are in 
adfacenr craters. If you tried to write a program that 
went through all These possible moves the tun-time 
would sake longer than was allowed for ihe comped' 
tion. So a solution should concentrate on the 
different positions the groups could «nd up in, The 
correcr number is |usi 168- 

A mistake a 3oi of people make is lo forget thai 
there is. no robot in the centre crater to start with. 
They then produce the wrong answer of 3 IS- We do 
not have The space to publish the full program which 
gives the solution. 

If you would like to see rhe program* write to u* 
and we will post you a copy. 

Congratulations to Jean Hanopp for trying 
hardest. 



Round 5 

Quotations 

1. "Out of sights out of mind" when 
translated into Russian by computer and 
back again became — what? 

2. "I don*t believe in maths" — who said k? 

3. "Chips with everything" — who wrote it? 

4. CF Scott said: M Television? No good will 
come of this device" Why? 

Round 6 

Can you find the well-known phrases? Stan at 
any letter and spell out the phrase by moving 
letter by letter into adjacent cells. 




Round 7 

What process does this Basic program 

describe? 

06 INPUT A,B 

10LETA-X 

20LETB = Y 

30 LET2 = 

40 IF B<A THEM GOTO 80 

50LETA = A-B 

60LETZ-2+1 

70 GOTO 40 

80 DISPLAY ZA 

90 STOP 

Round 8 

HFRE ARE FIV'R siore locations which were 

intended to contain oui Christmas mdMgE tti 
you. Unfortunately., they have been put in 
reverse order, At least they can be moved 
along the connecting wires in the directions 

shown. 




No location can hold two words^ so if you 
move Your to C&mpiwr for instance, you must 
immediately move Computer to From. 
From can then move into the blank space 
kfl by your first move. Can you put the 
message right in just one sequence of 15 
moves? Can you do « in less? 

Round 9 

IF VOU TAKE the digits of 1,634, take :h L - 
fourth power of each and add them all together 
you get 1 + 1,296 + 81 + 256=1,634 - your 
original number, There are two other 

numbers which have this property — what are 
they? 

Round 10 

The solution's are all in front of your nose! 

1 . It goes rude. 

2. Gog, your trump. 

3. React to no ham. 
4- Samj free person, 

5. Drop me 3 O comet! B 



A £15 book token will be awarded to the fust 
correct solution. All entries must be? at the 
Your Computer offices by The last working day 
in December, The result will be published In 

the February Issue. 



YOUR COMPUTER, DECEMBER 1381 91 




The ZX80/81 DESK CONSOLE 

inducing switches for cassette and power 
Complete and Assembled 

l Fit* 16 RAH on SQa ild ft I 



Fll i your £XH Of ZKfll 
Juki plug-in, NO Adoring 
Smile n#d ffrr SAVE/RUH/LOAO 

Bol h £• »**ti* and com p m *r r p u : s 
tiltod when naf hjiKllonil 
Switch fo# ^owf BV supply 
LED manlier for supply 



Fftltd wllh tuition cove 
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tig lit* 4t wr (not fluppl(*d) 

Slick flriir. flnith in AGS plMCk: 
BccaiMd lor m*nu.tl/ pencil 



Price C24,08 - E2,M p*p UK I VAT 
Send your Name. Address, SO or 81 , together with cheque of PO 

only for E29.99 to: 

TTL BOX 2, WARMINSTER, WILTSHIRE 8A12 7QX. 

AH orders acknowledged but allow 30 days tor delivery. 



Programs for your 

zxsi 



£3.95 



each [post free) 



from A. Parsons, 23 Coxhill Gardens, 

River, Dover, Kent 



1K Learning Fun. Learn spellings, add in hours and 
minutes, price quantities of groceries Of giv$ change, Pfus 
four function sums with whole figure answers and score. 
Plus Tables. 

16K Learning Fun. Add in words, work out areas and 
perimeters, translate between French and English or enter 
words in any two languages. P/us vocabulary and two 
versions of Hangman, 

16K Geography. Find towns in the U.K. or Europe with a 
series of five maps drawn on the screen. P/us Town and 
Country naming program and Engfish Towns Hangman, 

16K Art end Fun Play Noughts and Crosses, Battleships or 
Board Game against the computer, Pfus Draw a Picture- 
Print It if you have a printer, record it to display again, even 
add to it. Pfus two fascinating pattern generators. 

New titles continually being added 



Fuller FD System for ZX 80/81 






The Fuller FD System is not a Z X 80 81 add on but uses the micro board at the 
heart of a more powerfuti system, allowing the user to expand with the system 
or stop with a standard Keyboard ft case and using existing Sinclair 16K RAM 
pack etc, either way you only need a screwdriver to assemble the built items, 
the FD Keyboard simply plugs into the ZX81 which is screwed in position in the 
FD case, ZX80 installation requires soldering to the keyhoard.we will carry out 
this work at a fiaed charge of £10 SAE will bring you details of our products. 
Have your ZX81 Kit built by us FREE when you buy The FD Keyboard ,Case and 
Power Supply at £42.95 + £2 25p&p 

• FO Keyboard Kit £18 9 5 

• FD Keyboard Built £24.95 

• FD 16K RAM Board £39.95 

• Above items + 80p p&p 

• FO Keyboard/Motherboard add £1595 
to Keyboard price 

• FD Case £1175 + £1.25 p&p 




1 T« Fuller Micro Systems 
S.uiclf .rliJ Park Eu 5t 
Liverpool 112 9 HP 

1 tick zxso a 8i a 



Picas* sen** me 

I frnc1o» » cheque /jio lot 

Kami 

Address 



l 
i 
I 
l 
I 

i 

i 



82 YOUR COMPUTER, DECEMBER 19B1 



ZX81 



owners 

have you seen 
A book of 

30 PROGRAMS 

For Only £4.95 
NO MEMORY EXPANSION NEEDED 

Each program has been designed \q fit into IK gf RAM 

TEACH YOURSELF PROGRAMMING 

Comprehensive explanations of eecn listing win teach 
you many techniques of ZX81 programming, 

HOURS OF AMUSEMENT 

Wuh tides such as FORTRESS. BALLOON, and ODO MAN 
OUT, you could easily become a ZX81 addict. Plus, 
entirely new implementations of wellkngwn favourites. 
LUNAR LANDING. MASTER CODE, ORBITAL INVADERS, 
and many others- 

CASSETTE AVAILABLE TOO? 

If you order the book you can also buy the 

programs on a quality cassette for only 

£4.95 extra. 



Please send me: 

copies of the book at 
£4.95 each 

copies of the book and 
cassette at £9 90 pair 



Please send your orders 
with cheques/PO's to: 
Richard Francis, Dept.YC A/ S 
22 Foxhollow, Barhill. 
Cambridge. GB3 SEP. 



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111 

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EDINBURGH 



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SILICON CENTRE 

MAIL ORDER 
Price \m r ordar form on request 

Atari 400..., r ..,* £335.00 

Atari 800,.,..., ♦ . ,.,£635.00 

Acorn Atom 8 + 2K IkiX)******,**, +*,+*,*+,<+,<+**++, *+,* + ,*t14R0O 
Acorn Atom 8 + 2K (roady built) .f 174.00 

VkJeo Genie (16K) £329.00 

Video Gmie II . . £385.00 

V I Lr ZU i i a . l.i . .j ■ ■ ■ | l.i ^UF'MMhM f I I ^1 1 +1 I tl I f 1 lllllf 4 I 4 >■ - ■ l«K ' 03 i SKJ 

Epsom and Seikosha Primer 

Mattel I nteli vision, electronic games,, chess, software, 

books, accessories, etc. 

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21 Comely Bank Road 

041 332 5277 

ELECTRONICS FOR THE 80S 

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ZX81 ATOM VIC 



Make the most of your microcomputer with our popular 
range of proven books: 

D GETTING ACQUAINTED WITH YOUR VIC 20, by 
Tim Hartnell r with over 60 programs to get your VIC 

up and running from dsy one, .£5.96 

□ GETTING ACQUAINTED WITH YOUR ACORN 
ATOM H bv Trevor Sharpies and Tim Hartnell. 184 
pages, SO programs, including draughts £7.95 

D GETTING ACQUAINTED WITH YOUR ZX81, by Tim 
HartneH. Eighty plus programs in this 120-page book, 
including draughts..... , £4.95 

□ MASTERING MACHINE CODE ON YOUR 2X81 OR 
ZXB0, by Tony Baker. 180 pages, teaches machine 
code from first principles CB. 96 

THE GATEWAY GUIDE TO THE ZX81 AND ZX80, 
by Mark Charlton. Over 60 programs and routines, 
ZX BASIC explained in detail .£5,95 



□ 30 AMAZING GAMES FOR THE IK ZX81 r by Alistair 
Gourfay - , .... £3.95 

□ 90 RIP-ROARING GAMES FOR THE 2X80 and ZXS1 , 
edited by Jeff Wetnrich.„ 1H < £4.95 

INTERFACE, the monthly magazine published by the 
National ZXB0 and ZX81 Users' Club, in conjunction 
with the Independent Atom Users' Group, is just 
CB.50 for 12 issues. Sample copy, with many 
programs for each machine, book, software and 
hardware reviews, education, contact addresses, 
just CI . 



Please send me the items marked. I enclose £. 



1 ■ , v r i i - 



1 Vfl I r IB IHHi»»IH'PMI'.iim 

Address. ...*+<<. .*.+*...++ 



, i ri I I ■ ■ 4 + 4 II 11 + 4-1 I I IftM II P 



■ **.**■ 4I4 + + 4 I I I + + + -I 



VC 11 



Please make cheques payable to INTERFACE, and send the above form, or a copy, to: 

INTERFACE, Dept YC3, 44-46 Earls Court Road, London W8 6EJ 



YOUR COMPUTER, DECEMBER 1981 83 




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SEMINARS 



Tuesday, March 2 
Getting microelectronics 
into products 

Th i s semina r w i 1 1 co m b i ne the broad I y based experience of 

speakers who have assessed and advised on a wide range of 

a pp I icaf ions . w ith f hat of cornpa nies who have used 

microelectronicsto produce a new generation oi equipment, 

and who can Therefore comment at first hand on the technical 

and commercial aspects of such a traction. 

Chairman's hnl reduction 

Ken Edwards. Chief Executive. BEAM A 

Are designers responding? 

Trevor Gil pi n, E lee! rorves Applications Division Department ol 

Industry Overview and comments on UK industry s response to 

m c reelect ronrcs technology 

Identifying an application 

Ro n Wai n w rig nt , Pa tscentre I nternat tonal O bser va nons from a n 

organisation with experience ol identifying , advising on a no 

developing 3 p^i [ C^Tion^ of microeiecironics. 

Case Study 1 

M A Morhng Technical Director. Hamier 4 Srmmons Lid 

Mcroofocessor boosts battery charger technology 

Case Study 2 

DrE W Finh, Product Engineer [Industrial Electronics). 

Nor mateir -Garrett Lid Digital micro- ohm meifr rm proves field 

measurements 

Case Study 3 

Derek Pay, Sales Di'ector Tempatron Ltd Programma&ie 

controller ensures a market share 

Panel Session The day s speakers will answer and discuss 

delegates quesi ions. 

There win be ample opportunity tor delegates to i nspeel recently 
developed equipment which will De dismayed. 



Wednesday, March 3 
Microelectronics for 
manufacturing industry 

A large range of oW-the-shelf equipment employing 

microelectronics is now available to indusiry Morecanbe 

made to meet individual requirements, and new developments 

are constantly widening the scope for increased automation 

and improved control. No company can afford to ignore the 

world wide trend towards programmable devices m the factory. 

Chairman s introduction 

Ken Edwards, Chief Executive BE AM A 

Is industry grasping the Opportunities? 

Trevor Gilpin. Electronics Apphcalions [>vis*on Dfcparrmen! tit 

Industry Review of industry response to micros ectiwc 

rechroiogy and availably Government support 

Applications in the factory 

Da vie Foster. Project OHicer. Microelectronics ApoiicaiiC^S Unit 

U M I S r Whe re mic ros a re imdi ng use . pJus a look at points new 

users s ho ultf consider and possible problems 

The t ol e of the process controller 

Cfi r is G nttjths. MT E L imited . Whal PC $ Can now do * nd whftii 

i hey iaryi ndi no applications botn sophisfrcaredandSifriD^e 

Towards programmable automated manufacturing 

Professor Kesth Raihm.Nl. Roboticsand Automata Group. 

Cranefieti institute of Technology Technology now ewsts- and 

more is on the way - to help industry boost product ■, 1 1 

Microcomputer- aided design 

Or Perer Wilson, principal Research OHicer Ltcas Research 

Ceni re Low cost ent ry has widened t he appea I of CAD 

Panel Session 

T he d ay's speake rs wi It a ns wer and discuss delegates questions 

There will be ample opponumly tof deJegaies zo inspect recently 

developed equipment which will be displayed 



i REGISTRATION 

I 



Ptease complete »n CAP I TA LS and ret urn to ■ 
| Conference Administrator, Room 13 1 3, IPC Conferences Ltd 
I Surrey House. Throwiey Way, Sutton, Surrey SMI 400 

Tel 01-643 6040 Ext 4890/4892 

Please reserve placets) lor \ he Electrical Review Seminars 

I to be held at the M et ro pole Hoi el - N E C . Bi r ming ham on Tuesday 
| and Wfcd nesday Ma rch 2 and 3.1982 

The tee is £i 50 olu s 1 5% VAT (£22 50] per d elegate for bot h days 

and C90 plus ii% VAT (Li 3 50) per delegate tar one day An invoice 
I win besem. This includes ui tendance ai ihe conference, 
I documeniation morning eoKee. lunch and afternoon tea 



Mr/htii/kAti 

Posjiion 
M'/MrS/MiSS 

ftvtM 

Please send coniirmaiionol tootangs to 

Mr/Mr^Wiss 
P09lJ0n 

Company 
Address 



V-;| ':■!>- 



I 

I 
I 
I 






B4 YOUfl COMPUTER, DECEMBER 13S1 






Adtfa Computers Ltd., a maior supplier of computer systems 
to industry and business, have opened the Vic Centre in 
WgsI London. Here yog can see r discuss and buy everything 10 do with 
the new VIC 20 personal computer — in person or by mail. Hardware, 
software, lechnical advice and information is available from an experienced 
staff of experts. Even if you already Own a VIC 20. get on our mailing list to 
fcnow afrout new development s r Remember— everything has the backing or 
Adda's reputation, and there s a full 12 month warranty on ail hardware. 
The Vic Centre is easy to reach— Just off theA4Q. dose to North Acion lube 
tion 



Not just a computer but a whole 
expandable system 



T*3B 



AT ONLY £189-95 incVAT. Special cassette deck 

£44-95 incVAT. 

The VIC 20 rs a fuNy Hedged, easy-to-use computer. It** the core of 
a great expandable system, with lull-size keyboard operation. 
First-time users can work it immediately wilh plug-fn program 
cartridges, using your own colour TV to get up to 24 colours On 
screen- and Ihree diflerent sound tones. Or write your own programs 
in BASIC The VIC 20 lets you build a system as needs and budget 
dictate. You can expand its memory to 32k Byte with Plug-in 
modules, and transfer data to external storage units. So the ViC 20 
is more than jusi a personal computer— and Ms system will expand 
to put M eve<i further atiead. 
VIC 20 Dot Matrix Printer 

Tr actor- feed. 80 character-per-lme, 30 crwaciers-per second printer. 
C 229.95 incl VAT 



S - 9 * n *' 



£56 35 met VAT. 



VIC RS233 INTERFACE 

Fully implemented ilueleveisi 

RS2&2C-V24 

Gl DIRECTrONAL INTERFACE 

AMOwS ViC to wOf h. as trfainif jmc Terminal 

Drive a Qume Daisy^ne^ or a Paper Tape 

Puncn elc, elc 

FEATURE this umi contains maslei powraf 

Supply wFucti £uppoi Is VlC't own supply 

when cat tying Memory Expansions. 

Cassette bfpyes Lughl Pens, Printers eic 

VIC-MEMORY 3K 

SmaM sszg— 'G'/Aust rnemofy escpans^on 
Plugs inic tfic and reproduces memory-pori. 
Can b* used wi|h oirrer espans^On-S gi^es a 
loiaa ot $k user static ran on ViC 
FEATURE Tnis Poard allocs Vic eo move 
Bas>c to D*0 ,ri a l 103 £ l$0*u"u- as m Pen. 
and enables the use of high RESOLUTION 
COLOUR GRAPHICS OT-Z5 mci VAT 

VIC TOOL KIT t2fi_7£ incl VAT 

For tnow who know tqor hit on Pet wu now 

nave same labilities for Vic. 

ftenumoer. Ay So, Append elc. 

This may be used wW the slacK VJC Rom 

S.vi'i.n Huarii 

VIC ROM SWITCH BOARD £40.25 incl VAT. 
Arr inexpensive unit wmch plu-gs direcE on so Memory 
Expansion Po'i 0* tfte VIC »™J allows the insertion d up 
io 4 fiOMS ior games pack* or tooth it aids, eic 

FEATURE. Simple aoflware switcn axchanges each pair gT 

ROUS into VIC s ROW space allowmp clashing ROMS to be 

used 

FEATURE. Plug-in ieio lorce sockets are available as Optional 

enras lo help el im male pm damage; to valuable ROMS 

TERMS AND CONDITIONS, All poods sow Su^ed lo Adda 
terms and condi lions ol sale. Full deiai's av^p able 
on request, but include- 7 day money bach guarantee. Adda 
12 month hardware warranty Please allow ?t days tor delivery 
Allow 7 days tor personal cheques lo be chared. Quoted 
tfficei Are inclusive ol VAT 



1/r 



VIC UGHT FEN 

This hign quahty hgnt pen ^orfcs m both 

normal and Hi. Rgs modes on rim Vic 

allowing simple interaction with mp Vic 

wptnout keyboard entry. 

£a*y lo prg$ram and easy lo uss. 

eg. Menu selecdon Non-kGyDoard entry 

Teaching Games. 

FEATURE touch sensitive. ■■ Enter"' contacts 

lo e^mmalt accidental entry. 



vie Games Port Adaptor ctuie 

games pO*t plyg 

A two into one adaptor lor use wrlh bom 

jOyiticM and light pen?, A must tor those 

who require Jul* control ol flames with 

Afaph-'cs 

P£ATURE ?ow-eosl High quality. Rabutt. 

VIC JOYSTICK 

Siftfl , 

Ha nd- He Ic joystick units lor games use f 
^vin^te Ml Pair or Single canriflur3H0r> L 
N B (2 Singles w*n f\u\ work as a pair * 
unless modi lied i 

Le Stick £3075 mcJ VAT, 



£2*.75 incl VAT 



E1*.9S4HC^ VAT 



^ 



tUM incl VAT 



Thi u-*rimare}oystick. On* handed mulfj-direchonal super 
sensitive stick *nh bunt in lire bull on 



VIC software Each of these tapes £14.95 incl VAT. 
Codeb r ea k er l Code m a ke r 

You o^ay thr^ VIC or ine VIC plays you in lhis corrnpulerjsed 

version of Mastermind 

VIC Sea wolf. VtC Trap and Bounce oyf 

3 fun games, a submarine snoot out. a oea! the VIC and an 

oW fa^oupitfj pub game Good games wilh difrereri skill levels. 

Monster Maze and Maltas Hurdler 

A lun game wrth good colour and sound and a mental arithmetic 

learning game Highly paled by everyone we have Shown it to 

Hardoi lhanyqu irimH 



Goods flequited 



Price 



Add £2 00 p. \ k f l-' 
orders under L50 00 

Njtp .^ 

Address 



' ■! 



MAIL ORDeR to: Adda Gompulers LirTnl«0. FREE POST. London. 
v £ ? W13 O0R of telephone youi ordor |24 hours a day> 10 

01 09? 0904 quoting your BARCLAYCARD OR ACCESS 
number 

1 1 wicl&u i thrqup mada 

vAyaWc Ic Adfla Go^c^r-rv 
Liiiil^d rrv 

t 

* ftww ewe* <*tf Bj'curAcc**> 






SHOP ADDRESS Adda Comoulacs LintFtad, 

i54 Viciona Read. Acioi London v& T# I OlftW ^04 

OPEN l0*m — G om rTyesday- Frut^v *0 ^r— f pm |5>3mjr03yj 



Mi 



YOUR COMPUTER, DECEMBER 1961 8& 




1- \ 



1 S^wr, 



WHWm 



i— i 



wtf 



?Pi 



bm 







OPT^ 





April 23-25, 19B2 
Earls Court, 
London 



\ ,. \ v ■■**. 



„.„,. Brtnpra 



? v 



J 







nlT 



Personal computers 
Home computing 
Small business systems 



1 -;<.<« 



L 








. . a// wa/fcs of We p personal computers have 
revolutionised computer power — bringing it 
within the reach of a far wider ana more 
popular market than ever before 

In 1982 this revolution witt explode onto the home 
and personal computet market To meet thts 

demand. Practical Computing and YQur 
Computer announce a brand new event— The 
Computer Fair The promotion of the exhibition will 
be heavily geared to attract the growing market of 
potential and existing users of personal computers, 
from home computer enthusiasts to businessmen. 

Bring your computers and services to life— alt 
walks of lite— at The Computer Fair! 

Complete and return the coupon — we'll send you 
details. 



i 
i 



(gmputi 



>/ 



/ 



Exhibition Manager. 

THE COMPUTER FAIR, 
IPC Exhibitions Ltd.. 
1. Throwley Way, 
Sutton. Surrey, SMl 4QQ 



Name 
I Position in Company 



_ Company 
I Address 



Tel. No. 



96 YOUR COMPUTER. DECEMBER 1381 




New and popular 
Sams books 



Mitchell Waite and Michael Pardee 

BASIC Primer 
£8.35 672-21586-1 

Mitchell Waite 

Computer Graphics Primer 

£10.45 672-21650-7 

Stephen Murtha and Mitchell Waite 

CP/M fM Primer 

£1045 672-21791-0 

Leon Scanlon 

6502 Software Design 

£9.05 672-21656-6 

Andrew C, Staugaard, Jr. 

6801, 68701 and 6803 Microcomputer 

Programming and Interfacing 

£10.45 672-21726-0 

Andrew C, Staugaard, Jr. 

6809 Microcomputer Programming and 

Interfacing with Experiments 

£10.45 672-21798-8 



Jonathan Titus, Christopher Titus and David Larsen 

TRS-80 Interfacing: Book 1 

£7.65 672-21633-7 

TRS-80 Interfacing: Book 2 

£8.35 672-21739-2 

Elizabeth Nichols. Joseph Nichols and Peter Rony 
Z-80 Microprocessor Programming and 
Interfacing: Book 1 

£9,05 672-21609-4 

Z-80 Microprocessor Programming and 
Interfacing: Book 2 

£11.15 672-21610-8 

Prices are correct at the time of going to press but 
may be subject to change. At I titles advertised are 
published as paperback books. 

Dealer enquiries are welcome: 

Please contact Roy Jones at the address below or 
telephone Hemel Hempstead (0442) 58531 



Prentice/Hall «f**ifi International 



Sjrm Books Stockists 

B**jrm%* b Electronic NUcNnoi 

* Strati 
I 

Byt#*r\oo Compufftrtarid Ltd 
PG I 
St Hi 

Cambridge Computer Store 
1 Em many* $****' 
Cambridge 



66 Wood Lane End. Hemel Hempstead. 
Hertfordshire HP2 4RG, England. 

Exclusive distributors of Howard W Sams books in 
the UK and Europe. 



Datron Mlcnp Centre 
UJih^m kouit 
2 Abb#vri.ilg florid 
Sheffield ? 

Micro-C 

S-t 1 Marnn#du W*v 

Union Street 

ftiinmrighinT 

Micro- C 

Unn 2. Chinnon* Hill 

industrial Etiaie 

Funpondf 

fer i s Co I 



Micro-C 

57-59 Altawi Street 
Leecfi 

MiCffrC 

127 Charr« Street 

Leicester 

Mkro-C 

Urius 91-93 Arodiie Contra 

Luton 

tadlcxntahire 

Micio-C 

19 firowfi S [C##! 

Winchester 



Mil :ro C 

31-35 Blagdon Road 
New Maiden 
Surrey 

Micro- C 

2 Wheeler Gale 

Nc*ttirsgihnn 

Mkro-C 
10-11 en'ijale 

Srnj!-«4imp|o^ 

Hampshire 

rVawbaar Compulin^ Store 
40 BarlhpJ^niaw Scifrei 

Nowburv Bertihi?! 



Silicon Cert/* 

Pidaural Eleclrortidi Ltd 
21 Com ft \y Han* Road 
Edinburgh 4 

Software Mcuii 

Hofsesh-M V*rd 
&rook* Street 
London WT 

Tomorrow * World 
Gallon Arcade 
Grafton Street 
L>iWn 2 



YOUR COMPUTER, DEC ^e IR 1961 87 




(Mmnat 



B.B.C. ROM Sets 

Single Floppy 
Disk Units (100K) 



Write for details to: 
the Acorn Specialist in Yorkshire 

NflW Hardware 

" ACORN Atom* Bil- ,„ , fwnClWOO 

■ ACORN GP 80 Print* * Cable M 032 00 

^ ATOM Word Pact ROM m „..C».O0 

' ' |M|raM45mQrvri*w l K to ecomrancted I „.,... ._...„,. £3 2D 

New Software from ACORNS OFT 
* GAME 1 A*t«fouJ<i * Sutihiinr * Breakout , E1I.SD 






Ell JO 

£11.50 

„.m.so 

,...,£1150 

■ i ............ L 1 1 .50 



' GAMF 3 H^t T<ap * Lunar Lar-rfcr - Black Bo* 

■ GAME4Siai 1npfc i FcJJr PW- I Space An*ck 
' GAME 5 Jnv&dtt* i WtjifPptH * ft*wtt <..*..,.. 

* tiAMFE Dodyems t Stooti » Anx^fra...^...., 

' GAME 7Gr**n Thirds i Raliisiics ' Snake. ..... ." .' . !~~!~„tll 50 

" GAMES Stwgate < Go i Mok^j * fiohot* fH.SQ 

" SOFT VDU New chancier sRt design ... f 1] 50 

1 MATHS PACK 1. MATHS PACK 2 „„. .„.. £!1 50 

■ UTILITY PACK 1. Dfeftfwnfall * F^T COS - flgnumbef...... Hi. SO 

' ATOM DATABASE. Vflfsaiile ft efficiont tllM 

' PEEKOPrDcesscr Sinu^tes nn cre»- <,,>. ...... £ 11,50 

" A TOM FORTH. FulMnpterTiimralian.. £11 50 

•ATOMFOnTH.Uwr-sGu.dfl... , . ,£5 00 



Books 

' ATOM Bkts-nessbyJ. PNpfjtA , ,_„ ,,,,, f 6 95 

* The ATOM Magic Birth. . a ,...., f 5.5ft 

*G*tiPng.AcquBintedwithyoiif ACORN ATOM mm £7,55 



Iff, 



ELTEC SERVICES LIMITED 

231 Manning ham Lane, Bradford BD8 7HH 

Tel: 0274 491372 




ADD A PROFESSIONAL 
KEYBOARD TO YOUR 

ZX81 

■ No de-soldering necessary 
— just plug in. 

■ Full travel keyboard as 
used by international 
computer and terminal 
manufacturers. 




nfietrfillif i 



£2&95 

inLlud'mq VAT 
pmt Br q*c king 



"All- you need" 
easy to assemble 
kit comprises: 
On** f^.TGe 47 key keyboard module lit ted bui not soldered to doubl t- 
Sided panted Circuit boardj connector*; simple plug m {legible cables: 
icrews. mounting feet and legends. Two- pari keycaps wilh butions 
pre-assemfcieci on keyboard ond tlear protect ivechp-on caps I Or litting 
afrep ingend* have been positioned. Comprehensive assembly instruct 
ions supplied wilh each kit. Allow 28 days for delivery. 

rpiease send ...... keyboard kTt(T}^^a^M~ + r^eq[Ie or" 

I postal order made payable to:- v€ No*. 

I"^|^ COMPUTER KEYBOARDS (dept. ) I 

| ^^J ^^^_ Glerwlale Park, Fembank Road, Ascol. Berkshire. 

I ^^ m ■ ^ m Phone a-LeaHel 03447 4731 

^hh^^^ Plpaw* pnsure voyr name and add too ara clearly ftatad J 




Sigma 

Technical 

Press 

The UK Software Publisher! 



New Boo**: 



BYTEING DEEPER 
INTO YOUR ZX81 



by Marie Harrison 

Th e Z X81 M rrr ora mpu ler is now, deba ted! y , c he fas I rst sol li ng 
pitrfOAil computet in (he U.K. Unfortunately, the user's 
man li a I cannot jnswer all trie questions and problem* I ha! 
arke when using the ZXB1, Aho, the tiwr\ manual gives the 
dMimt impression at being wrriten by 4r\ engineer, for 
engineers . . . not fot Ihe average user pi ihe ?X8"L The only 
way you can see Ihe manual is by buying the machine! 
BYTEING DEEPER INTO YOUR ZXtfl *upptemen<* th<* mi 
manual and provide* ^n excellent, imroduciion to computer 
programming, I; Marm 1mm tir^i pt inuplev and r by reference 
lo over 30 carefully graded examples, progresses I o some of 
Ihe most advanced techniques useable on this computer. It 
presents del ailed project and programs tur lht s user to waive: 
each at these is suitable lor dome* r re uiefe.g. parties, personal 
data banks, and homework aidsi. 

090510413 7 December 1951 lS0pa»ei id.95 

PRACTICAL PROGRAMS 

FOR THE B.B.C. 

COMPUTER AND THE 

ACORN ATOM 

:i\ David Johnson-D4*ie* 

\p ;! i. !v ,.,: \r, '\iinr, ioi use -rrr. r h.> VTOM thff book 
con I a ins 20 practical programs for a wide range of dilfefeni 
applrcationi. ranging from mai hematics and graphics, id 
language manipulation, and games. The programs are 
explained in great detail so they can b* Tailored lo inrjmilujl 
requirernenls + and many of I hem could b^ translated lo run on 
other micro compuKirs, 

The book i^ i mended fo^ owners at rhe Acorn \ I OM and BBC" 
Ptoion who understand how to e..ier and tun programs, but 
do not necewanly consider I hems elves lully acqu aimed with 
BASIC or machrne code. Many of ihe programs will run on 
minimum ATOMs h aJ I ho ugh Mime of the programs require a 
machine iviih the full 12k of memory. 
90S 104 1 4 5 Decern ber 1%1 1 25 pages £ 5,95 

P/easc wrilv for full dcizih of rhe SIGMA forthcoming 
publishing programme to: fohn Wihon, PwtfVCl MjtnsRpr. 
John Wiley & Sons Ltd-* Bailim. Ljne. Chichntvr, StMse^ or to. 
ht. Gnthito Seech, Sigma Technical Ptess. 5. Allan knatl. 
IV J f n i\ ft i w , Vj j m h ire. 



Distributed by 

John Wiley & Sons Limited 

Baffin* Lane Chrche^er Sussex POl9 1UD 
England 



6S VOUfl C0MPUTFH. nFCEI^RE^ 1961 



n 



: fl & F 50FHIMRE $ 



F 



PRESENT TWO NEW REAL TIME GAMES 

FOR ATOM USERS 



EARLY WARNING 




POLECAT 



m 



(H ,. !! 



Hnf 



BK TFXT h 6K GRAPHICS 
Destroy !h«? a Hacking wave of 
ICBMs -sing a radar tracking 
system and intercept missies. At 
each atTac* wave be^orms pro- 
gressively harder. 
48 levels - «mncl score and 
ievf*i counters 



6K TEXT £6K GRAPHICS 
Avoiding the hungry Polecat, 
make your way through the 
rrwe to the surface, and steal 
the food growing th^e^e. The 
maze changes when all The avail- 
able food has been relumed 
home, Millions of random mazes 
ano 1 auto score- 



Price: Early Warning; £4.96. Polecat: €4/95 OR 
Both Programs on one cassette £8.50. 
Dealer Enquiries We/come. 



ORDER FORM 

Send cheque PO payable to: "ANDERSON" EoA&F SOFTWARE. 
rOWILPSHIRE AVE., LONGSIGHT, MANCHESTER M125U 
:i)6i 243 7195. 

Return Name & Address 



Cadi- Ne 


Progrgii Ti(l* 


Oty 


CKHOO 


P**rat 




GOT01 


Lirfy Warning 




ODSfiO 


Ftitecat-' E»riV 




f 




& PO^o 




P*ogf*fn Lrtt 






F 




^ 


7"! 1 .! 




•"^ , ^ 


»r> mi 








• 






H 19 









£,189.95 inc 1 udi n g ua.t 



TWICKENHAM 
COMPUTER 
CENTRE LTD 

01-892 7896 

01-891 1612 



i Fi 1 1 1 1 rmrh 



72 Heath Road Twickenham Middlesex 



Have you bought a ZX81 ? 
Now here's a cassette 
recorder to match it ! 

The ECR81 Enhanced Certified Recorder from MONOLITH is a major 
advancement in cassette recorder technology which minimises the 
problems associated with standard audio recorders. This is a high 
quality proven cassette mechanism, enhanced to provide just 
the right signal levels to ensure reliable read and write data 
transfer between the magnetic tape and vour ZX81, 

• Each ECR81 come? complete with its own individual 
cer ii I [cation tape r tesied and serial numbered to prove your 
"nachlnfi reliability 

• rtfJ enhancement circuit board with phase - locked - loop 

oi and signal shaping tor peak performance. 

** MONOLITH ELECTRONICS CO U0., &/7 CHURCH ST AeET r CREftlLCMlt, SOMERSET 



Nil ■ c r rrwiiqih. 


fri« 


Tu.u' 


rOtv > MbAo4Mh ECU 81 Eft**nc«l€*riil«4 flrafdtili) 
*&^ . 2r*B>Arthfr 

»™^„ IPfeiff indicm Hunt ■ Tvp*) 


147 SO 




1 frit* sr&em aotfiqe & P*e* -ng Dtf ntcOtftf 


ftN 




Pricti includr VAT £ 


1 


Plrraprml rncninciuMT^i m 






£47* 



Including VAT. 

complete 



ton*- Mr. HruM.it 
Ad*ns 1 1 1 1 



i I I I I I I I 



U_ 



I I I 1 1 1 i I 1 I 1 1 I 1 I i 1 I 



L LJ I I I 1 IJ 



I ! I 1 I 1 I II I I 1 1 



I 
I 

□ ! 



m A long life heatf is fined, marched 
10 TDK CrQ2 hSgh bias r super 
avilyn casque tape*, 

# Mains St DIN connector leads provided. 

# Certification of tape head alignment - height and azimuth. 

• Certified tact tension, torque and speed. 

9 Fiji forward and rewind tape search controls, 

Th« ECR81 is a too suitable for Sinclair 2X80 and many ofhvr 
pGT^nal computers tttfflf audio recorders. 

• Please allow up to 28 days deNvery . • The ECH81 ti 
backed by our 14 day money -back option, • The ECRS I is 
not suitable for audio reproduction* 

MONOLITH 

electronic products 

Telephone: Crewfeern* 04S0 74321 



YOUR COMPUTER, DECEMBER 1981 89 



Britain's Leading Personal Computer Magazine 



Practical Computing is read by businessmen, scientists, 
administrators, teachers, students. In fact by everyone who is interested in 
personal computers and wants to know more aboul them . . , 

More about computer equipment, DowrMotarth reviews of personal 
computers and [>efipherals such as printers^ terminals, VDU s and diw: drives. 

More about software. How to write it. What to look for in business 
software. Evaluations of software packages to take the guess-work out of your 
software purchases. 

More about applications. Whal can you do with a personal computer? 
Case studies of the ways in which people as diverse as businessmen, 
manufacturers, doctors p scientists and teachers are using compulers in their 
everyday work. 

More about games. Designing your own games. How to achieve better 
graphics, Games and program listings to run on your own computer. 

It all adds up to colossal value. The best and most informative selection 
of articles and regular features about personal computers for only 80p a month! 

Practical Computing is available from leading newsagents. 
Or complete the form and return it together with your cheque/postal order to 
obtain copies on suhscriplion, 

To; Marketing Services Dept^ Rro 3 16, IPC Electrical Electronic Press Lt«L, 
Quadrant House, The Quadrant, Sutton, Surrey SM2 5 AS 

Please send me a copy of Practical Computing every month for a year. I enclose 
acheque/P.O. for £10(UK)/S1 6 (Overseas) payable to IPC Business Press Ltd, 

[Name 



Address 















Acorn Atom 

747 




FLIGHT SIMULATION PROGRAM FOR THE 12K ATOM 

Written for 8uy-byte by a 747 pilot. Accurate simulation of a 747 r s 
cockpit display [airspeed, altitude, rate of climb, altitude, flaps-j 
etc., and graphic display of horizontal situation El attiludel; allows 
you to gukle your craft to fhe landing strip. On making your final 

approach the display changes to a high-resolution 3D 
representation of the runway coming up to meet you. A real test of 
skill. Finding the runway *5 qirne a ehattenge - landing safely is 
even more difficult. If you succeed, you are awarded a skill rating 
and the chance to take off and trying again, 
REQUIRES FLOATING POINT ROM PRICE ONLY £8.00 




ALL FfflCiS wfiutsm 

TELEPHONE 051 227 2G*2 



E3 



9& 1WTHE ALBANY 



OLD NAIL S1HEET 



UVEflPQOL i.3*£P 



Acorn Atom 

CHESS 



B 


QOQS 


QflDS 


E 
S 
H 

3 


qDqQ 

■ ■ 


|D|D 


■ ■ 


JLP 


V. 


v. 


2 
1 


E*E* 


J3*0* 


*©&[! 


|i@4® 




ftBCP 


E F E H 



THE PROGRAM YOU'VE BEEN WAITING FORI 

Fantastic machine code chess game for in* 12K Atom. Features 
include: split screen 4 high res. + alpha numerics); many levels of 
play; castling £t en passant; computer plays black Of white. 
Supplied on cassette with instructions. PFiGE ONLY £9.00 

OONT FOBGET - OUR PRICES INCLUDE VAT & POSTAGE 

















p* f t jr*%. 










BUG- 


*"* V\ j"f 








■» +*? V 


■yyy ym-^-: y , 




9B tOO THE ALBANY 


01 D HAI I 



sssss 



LIVERPOOL U3 9EP 



90 YOUR COMPUTER, DECEMBER 1381 






^!S>@S)^a5>QUlC:>CSiLV A RESENTS A RANGE OF QUALITY 
<S@@§I@ HARDWARE / SOFTWARE FOR THE 

r® utt/j 

HMDYr'ARi All hordww* T* t*nl with complete instruct torn ond 

proo/o^ming Bw*"or«, . P'»&* allow 2S doyi for delivery * 

QS MOTHER flft. ZX-»/aT-»- OQjM 

E*t»ncfc tmiitii%g port to allow *ijr Rom Pack + two olhef toordi to be fitted 

On be-srd }V, Regulator ; Two 23 woy doyble i'0*d *dg* c^wdw for adflher*- 

Q5 3K_ftAW6D. " -— — ZX 80/61 - £18 : 00 



Reliable (pr*-**rv**V7 !• Static Rdm Board which combines with the Computon 
internal IK to give & tatol of 4K t Flvpt direct Inio Computer or Mother 8oord p 
QS SOUND 3D. — ZX 80/81 —— £25:00 

ApfOflfQfnmob'i lOund generator boOrd mrng th» vanoiile AY-3-rJ9l0 * 
3 PilchH / 3 Velum* / NoHi ioufc* / two 8 bir Input ; Oglpgt Porh / Envelop* 
ihapef « oil control I td from '|A£lC g Plugs into Ony **tarnal amplifier . 
QJ_QHAR *£ r -:*i 3Dl ZX 81 ONLY J- — £23 : 00 



Simpt|HTj*Ti iod {T cut ; I r«iiP« ; 1 *fr# } required to ZX-80 ,* 
GIvm two prso/ornn-afcU character lets of 64 ehorocT*fi each . Ui«t graphics 
kiv to ihrff o»'«#en the two let* . Um NO Rom ipace , Creole pour own 
chofacten - u >o«f and lower coj« alphabet ? selenitic ehorocten ; fine ITne 
graphic* : 7 -^:-n j gam** character* (not ipoce mvoder*j .. Works with 
•k Fifing EKOgroffli ondl wfth the Printer « Price includes Oemo Couotte p 
QS CONNECTOR. ™ — ZX-B0/ai ™ ,C 3 = 00 



Com In c?* '*o 23 way double ilded edge connectors bock to bock m On* needed 
fw cry y c QS EfcponfJons . ;T*c*pr Rom Boovdi } 



.SOFT*' Aft E --—*«*- All *O f Twor# Fl f»COfd*d twice On high quolily cotter r* 

and ip vint complete with fyil opero'lng Instruct Tom . 

QS DEFENDER, — - 2K RAM mlnTrmjm » 4K or 8K ROM 'Llll! 

Fat, Flicker free f Machine cod* , Moving graphics v»nlc-n of Arcade Gome, 
Mat couple* movfno gropMci gem* v*f for 2X-CompuT*n » Up to 84 Fat 
moving charocf*n on icr**n ot one* r FFnf ond only full icr**fi dFpploy r 

QS LIFE, — #K RAM Minimum Zm-81 ONLY £4:50 

Fat program wlrh Machfn* Cod* e*ll g*n*rotFor* ond ier**n dttploy routFn* . 

Sfmulat*! thi growth pi living caIIi In o 20 * 32 Matrix * Random pr ^rpgramm*d 
itart position* plyt M/C royttn* mok* thFi a Fat # compltx arid vor!«d program , 



Sknd S F A, 6 + for FULL data ih*«n on all hard won ond ioftwor* F Ch#qj« 
mob* poyofal* Fo 'Qulckillvo' and ord*n tint to ths FollowTrig oddr*ii 
QUICKSUVA^ 9$ f UPPER SROWNHILL RD,; MAYBUSH : SOTON : HANTS. 



■»■-■*<■* 



J 



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THE 



BUFFER 



MICRO SHOP 

(NEXT TO STREATBAM STATION) 

* • * 

MEW SOFTWARE SHOP EXCLUSIVELY FOR 

ZX81 

PROGRAMS, GAMES, "ADD-ONS" 

• * * 

MOST OF THE MAIL ORDER ITEMS ADVERTISED IN 
THIS MAGAZINE AVAILABLE OVER THE COUNTER 

• * * 

LOADING PROBLEMS? TRY OUR INTERFACE 

BUSINESS &TECHNfCAL DATA HANDLING PROGS. 

PROPER KEYBOARDS; CONSOLES; VDUs 

* * • 

DUE TO OPEN 

1st DECEMBER 

BUT, PLEASE RING 01-274 6674 FOR 
CONFIRMATION AND FREE CATALOGUE 



CAMBRIDGE LEARNING 

SELF-INSTRUCTION COURSES 



Microcomputers are coming - ride the 
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0,0 systems ltd. 



A/D BOARD FOR NASCOM 

* 8 input channels 
■ 3Q miscrosec conversion 

* Over voltage- protection 

* Prototyping area 

Price £13S + 



* S bit resolution 

* Sample gnd too\<S 

* Full flflt/interruoT control 

* NASBUS compatible 
15% VAT <post free) 



GRAPHICS BOARD FOR NASCOM 

* 384IBI x 2561 V3 high resolution graphics display 

* fully bit mapped * Mixed text and graphics 
« Full software control • NASCOM 2 or 4MHz 

NASCOM 1 

* Graphics software supplied 

Price £E5 + 15% VAT (post free) 

EPROM PROGRAMMER 

■ Programs 3 fail: 2708/2716 
Single rail: 2508/2758 

2516/2716 
2632/2732 

■ Software supplied for Read /Program /Verify 

* Can be used with other machines with 2 parallel ports 

Price £63 +■ 15% (post free) 

DUNCAN 

* Fast real time interpreter/ control language for NASCOM 1 or 
2 (please specify) 

Price £12 + 15% VAT I post free! 

MEMORIES 

* 411G-1£0ns95p each + 16% VAT [min order 8\ 

* 64 K- 200 ns £10 each + 15% VAT 

MONITORS 

* SMC 12" green phosphor - 18MHz 

Price £175 x 15% VAT (carriage paid] 



6 Laleham Avenue, Mill Hill, 

London NW7 3HL 

Tel: 01-959 0106 



miCRDflGE 
ELECTRDniCS 



* Personal Computers * TV Games 
* VCR's* Printers* Monitors* Software 

ATOM'S and DAI's 
ALWAYS IN STOCK 

Complete range of Atari games. 

Open Mon - Sat 9am till late. 

Credit cards welcome. 



NEWTHIS MONTH 

SS, £10 OFF 

£5voucherongoodsover£100 
£5 voucher when you introduce a 

new customer 

The Seikosta 96 ASC 1 1 cha racter 

pri nter only £1 99 inc. VAT 

Pa per and cable free. 



Send for price list and mail order details. 

135 HALE LANE EOGWARE MIDDLESEX HAS 9QP 
TEL: 01 959 7119 TELEX S81 3241 



ICRO-80 



UK Subscription Dept. 
24 Woodhlll Park Pembury Tunbridge Wells Kent TN2 4NW 

WE ARE PLEASED TO ANNOUNCE that MICRO-80 is now available in the UK in 

CASSETTE EDITION. 

Each month we publish at least six programs for the TRS-80 or VIDEO GENIE 

and ( 1 1 

SUBSCRIBERS may now have the benefit of receiving their programs on cassette 

for IMMEDIATE LOADING. 

WE ARE ALSO CONTINUING our special offer of a FREE cassette program to all 

new subscribers who complete the coupon below — even if you order a 

subscription to the magazine only. 

Please enrol me for an annual subscription and send me my FREE cassette program. 

I enclose £16.00 ~j {magazine only) or £43-60 G (magazine and cassette edition). 

(enclose your cheque/P.O. made payable to MICRO-80 and send to the above 

address) 

Software offer, and cassette edition prices applies to U.K. residents only. Overseas 

subscription rates on application. 

Name 

BLOCK CAPITALS PLEASE 

Address 

VC 12/S1 



92 YOUR COMPUTER. DECEMBER 1981 



THE 



Video Genie 



6G30O0 Series 



WITH ■ l&K um- AA VI pirn *-<ie*d#d 12* M.trMtifl BASIC Id flOM 'My TAB BOLfrrf II son 

WaW C&mjj*5"t* " H -J* 'l^pe of iOTetol'e HffrMv i***Wf *Sflff frOnTiilatd. PSU. UHf 

\mtjtiufatw , and c»»ne " S^t> v pfaflt Ml 
^tieo moftiitv at UHF TV ■^v* eipenwn ;o 
■ V rt«»ki t ir*d p*-n|if fl AD«Ajltlv iomplili 




16K 



£299 



4 VAT 



6P80 



The mo si compact 80 column impact 
graphfc-dot printer available- 
at a very compact price 



Graph ^ NorrtMjl and 
Cfayfe ■■ ,ViJth Characters 
can be Grimed on the 
same line Pine f eed 
Tractor i£ equipped as 

S[an£jrfr^ 

Two L>ne Feed 

Commands ( 1 r 6 arid 

1 9 inch) 

Pnnt on Plain Paper with 

rwo copies 

ConiinuQUS S elf -inking Ribbon for easy handling 

C*rn ironies typr? PaidFicI lMerfacesfartdJJ 1 d 

Wide Range of Optional Interlace Boards 

Self Test Prog* a-nme standard 




£225 



+ VAT 



SUPERBRAIN 

Supveram'i CP'M operating iyiwm 
boail* an avfrwhplming jmpunt gf 
a .liable jotTwaro m BASIC. FOR 
TRAIS. COBOL, and APL. Whalflier 
your application Garwal Leoftur. 
Account* npcaivabic, Payioti. in«or»- 
[ckv Or Word Processing. Supar Brain 
it too* tn <t* class 
320K £1850 700K E2400 
1 5Mb £2750 



COMMODORE 
COMPUTERS 

PET8K £415 

PET 16K C525 

PET 32K £650 

PIT 8032 £895 

DISK DRIVES 

4040 £696 



PRINTERS 

EPSON TX8QB [inc. 1,'F & 

cable) £299 

EPSOM MX80T £395 

4NA0EX DP8000 £495 

-NAD&XDP9500 £895 

-NADEXDP9501 £995 



VIDEOMONITORS 

10 BLACK & WHITE £85 
10 GREfcN SCREEN £96 



Acnlab 

Floppy Tape 

The tape that behaves 

like a disk. 

Connects directly to TRS-80 

level 2 keyboard. Operating and 

lile handling software in ROM 

B commands add 12 powerful 

functions to level 2 BASfC. No 

buttons, switches or uaJyme 

i -o-nroia Full control of all 

functions from keyboard or 

program. Maintains dhrectory ^ith 

up to 32 files on each tape. 

forallTRSSO 
& Video Genie owners 



TRS80 
version: 

Video 
Genie : 



£165 
£170 



Please add £10 Securicor 
delivery charge to all 
computers etc. 
Plus 15% VAT on all prices 




Simple to build, -simple 10 opera le 
A powerful, full facility compute* 
iMth all .he features you would 
expect. 

Just connect the assembled com- 
puter lo any domesiic TV and 
power source and you are ready 
tn begin, 

Full-SFzed QWERTY keyboard 

6502 Microprocessor Rugged 

infection moulded case 2K RAM 

3K HYPER ROM 23 integrated 

circuits and sockets Audio 



Acorn Atom 

V Unique in concept — 
the home computer 
that grows as you do! 

Special features include 
•FULL SIZED KEYBOARD 
'ASSEMBLER 

AND BASIC 
•TOP QUALITY 

MOULDED CASE 
•HIGH RESOLUTION 

COLOUR GRAPHICS 



cassette interface UHF TV out 
pu 1 Full assembly insl rue I ions 



£120 



+ VAT 




The Second Generation 
Personal Computer 






Highest performance lowest price 



'4eK(8Q80Aj 

- 16 Colours or shades of Grey 
m Multiple High Resolution Graphics 
Modes 164x71, 129 x T59 H 256*335) 
■Character mode 160* 241 
* Split Screen Modes 

Wk A V Personal 
Ummm Computer 



* Full ASCH Upper & Lower 
Character Sel 

* U niq u e graphical Sou nd 
Commands for Smooth Music, 
random frequences h 
enveloped sound 1 

•RS232J r 
at only 
+ VAT 



£595 



Paper Tiger 460 



t}¥ •nco^^afasng mjnv fe£[uri-a pi*tf>OuVr 
On** a^*ii*bat Dn'u^illS'ClM^^flrnycr'^Qfe 
Ff Jluitt ilk t* a H>«iflllV iJevrliipecl -.ii^e avife s'iy^e'^O IQ-umP head -&-*»£*- OWL*pf 5** fle:> 
C* *flCh iThplui cfti'tclc wHP< jijil ani- paui or ih* pi miUMJ giving i dense *.q" 3U»li1a- |WH 
■'nage A-ithoul «educmg the umls 160 c p,5 pr-ni speed 

H alio cyf'pri i tn direc-tiQrtii l^ic Mekmij device to ennjoGi iti prmt oflbmisji^n th*i«te' 
i-ttics a'd iMde 'an^e cf\ p- 1 n: v e" taciiirv reacurfc s.jl^ j-i f^orio * propofinxial spacing, auio- 

itiPim. (lu^iltJliDn pi-oyrdi'iniiable «>Qnf Cwilai a nil tffir.ii- UbCMiij *Ad '1iW fMuEi&f¥tng »Oa 
s- ■■! : " ■ ■■■ ■.Fj-i-;:.ii.^ , ii" 1 , 



Paper Tiger 560 



£785 * v * T 



th* PjfHf-i t«fler &i$0 I* the tint pnnter w h c»^ bnopei ir*e ^ap l»twwi pornw^i^nii imim 

»nd daity rt-hcrl ryp^s *"cn ^9 aua^ty pr^bn^ #e .1 rti^iiveiv lev. u"ce 

Fyll 'w>dlh' !3? rdlij^n pnnT.ng nr l&D [j •; a un^ue ^n« w -,ft i lagged pf^nl head, b 

rl'Tfcl'-nn^l priiEing. #n mhui'ir KaAIw fmst .inff J '1ui1 Ql t«:et:CJtHe lealurei let it ap*?t <idbt. 

p*dinarv mjilni onnl-Pis 

PXri (&i *u*r greirw vefsatrhrv a ruti doi ©lot gr#pi^cf 

liciliiv if suppi.ed *^ic-h mciudei j ?K j __ _ , 

Dun*. Ollttat * VAT 



£995 



Boobs & bits 



Books Manuals - Diskettes - ribbons - Paper 

- cnips 12114 x2 IK) £4 pair. 

RS232 10 Centronics interfaces £40 etc. etc 

A variety of second-hand computer equipmenr usually available, 

spares, repairs and service. 



29 Belvedere, La ns down Road, Bath BA1 5HR 
Telephone: (0225) 334659 



YOUR COMPUTE ft, DECEMBER 196? 93 



The Exhibition 
Which Works 
For You 



mn 



:3. 



WEST CENTRE HOTEL, 

LONDON 

FEBRUARY 24-26, 1982, 



Over 6300 quality visitors 
attended the 1981 show — 
providing the correct balance 
of users and specifiers of your 
products and services. 
The formula is right — you 
can make MICROSYSTEMS 
"82 work for you by 
reserving your stand 
space NOW 



Find out how exhibiting at MICROSYSTEMS '82 can work for you by 
completing and returning the coupon now, to: 

Exhibition Manager, MICROSYSTEMS 82, IPC Exhibitions Ltd., 
Surrey House, 1 Throwley Way, Sutton, Surrey SM1 4QQ. 



MICROSYSTEMS 82 Is 
sponsored by Computer Weekly. 
Systems International, 
Practical Computing, Your 
Computer, Computer Taik, 
Of ice Systems. Data 
Processing and Microprocessors 
and Microsystems 
and organised by IPC 
Exhibit ions Ltd, 



Please send details of exhibiting at MICROSYSTEMS "82, to: 

Nam© ^ 

Position in company 

Company 

Address 



.Tel. No 



94 YOUR COMPUTER, DECEMBER 1981 



ZX81 16k SOFTWARE 



PACK 16/ 1 includes all ofc 

AIR TRAFFIC CONTROL: Animated radar screen of busy 
airport shown, you must bring planes into land; 
INVADERS SELF PLAY: PHONEBOOK - keep friends' 
and relatives' numbers on cassette; DATE J 81 — 
computer dating program. Who will it pick for you? 
ALL ONLY £4,96 



PACK 16/ 3 includes all of: 

INDI 500; video roadracer; DRAUGHTS; Computer 

Chequers; BATTLESHIPS - nautical warfare on your 

own computer, 

MASTERMIND - Brain Teaser, see if you can beat a 

microelectronic mind, 

ALL ONLY £4.95 



PACK 16/ 2 includes all of: 

ADVENTURE ATLANTIC: You may become very rich or 
you may be marooned forever; BREAKOUT: SQUASH 
PRACTICE; LANGUAGE TRANSLATOR translates any 
European language to any other; COMPUTAPR1NT — 
use this program to predict results of horse races, 
football pools, etc. 
ALL ONLY £4.95 



The breakthrough you've waited for: 

PROGRAM THE ZX81 IN ENGLISH!!! 

With GAMAL 81 you can now- write adventure programs 

in hours not weeks and with GAMAL 81 you'll have 

every adventure you'd ever want for the price of one. 

Comes on cassette with instruction book, £7.96 



All our software comes with full instructions and is SAVEd and ready to RUN, no 
need to spend hours laboriously typing in from books. 



CONTROL TECHNOLOGY - 

PERSONAL 

COMPUTER SCIENCE 




Cassette Vh 



A super value cassette of 16K and IK software written in 

Machine Code and Basic. 

Includes: 

React, Invaders, Phantom Aliens, Maze of Death, 

Pianetlander, I Ching, Hangman, Invaders, Laser Base, 

rectangle plus more. 

ALL ONLY £4.96 



Tapebook 50, Version 3 



50 programs for the IKRAM ZX81, 

Latest version includes: 

SQUASH, BREAKOUT, COLUMBIA. SPLAT. 

INTEGRATION, CREDIT CARD CALCULATOR, BANK 

A C. VATCHECK, TANK BATTLE, TORPEDO, 

HEXLOADER, BINARY CONVERTER, AND LOTS, LOTS 

MORE. 

Still amazing value at £6.96 the lot 



PACK 16/1 + 16/2 + 16/3 

(any two cmty £5.95) 

ALL THREE ONLY 

£6.95 



TAPEBOOK 50.3 + CASSETTE 1 V4 

BOTH ONLY 

£9.95 



BOTH OFFERS ARE ONLY £13.9 

CHRISTMAS SPECIAL OFFER 

TO ALL ZX81 OWNERS 



All prices include VAT and postage and packing 



CONTROL TECHNOLOGY, 
39 Gloucester Road, Gee Cross, 
Hyde, Cheshire SK14 5JG 
061-368 7568 



YOUR COMPUTER. DECEMBER 1981 96 



ZX81 SOFTWARE (16K) 



TfTte & DESCR/PTfQN CODE 

ZX81 BUSINESS SOFTWARE 
VIDEO-AD. Continuously rotating 
display of 16 pages of advertising or 
other information. Shop window/ 

c la s&ro o m /e*h ibition /semi ng r H 

VIDEO- PLAN. Financial modelling 
package. Scaled down to fit the 
ZX81 computer. Spaed for up to 
1000 x 10 digit numbers plus 
headings and titles. 

ZX81 SERIOUS SOFTWARE 
VIDEO-GRAPH. Use the computer 
to build pictures and merge them 
like an identikit. 



VIDEO-VIEW. Your own personal 
and private version of teletext/ 
viewdata. 

VI DEO -MAP. A game with a serious 
purpose. A geographical tutor 
based on maps. 



PRICE 



AD81S 

(Std J 

AD81L 
(Lux) 


7.95 
9.95 


PLAN81S 

(Std) 

PLAN 81 L 

(Lux) 


7.95* 
9,95* 


GRAPH81S 
(Std} 

GRAPH81L 
(Lux) 


5.95 
7.95 


VIEW81S 
(Std) 
VIEW81L 
(Lux) 


5,95 
7,95 


MAP81S 
(Std) 
MAP81L 
(Lux) 


595* 
7.95* 



ZX81 GAMES PACKS 
FORCE- FIELD. Hostile UFOs attack 
a city,. You control the force field 
which destroys their bombs. 

SPACE-RACE. Party game for up to 
eight players. 

FOOTBALL-LEAGUE. For the 
student of football. Simulate an 
entire season's play. 

TEST-MATCH. For the student of 
cricket. Select your teams and see 
who wins. 

STOCK-MARKET. Buy and sell 
your way to a fortune. 

*Not suitable for 2X80 with SK ROM. 

Send iarge s.a.e. for further details. 



FORCE 



3.95* 



SPACE 


3.9S 


FOOT 


3.95 


TEST 


3.95 


STOCK 


3.95 



To: Video Software Ltd, 
Stone Lane, Kinver, 
Stourbridge, W r Midlands. 
DY7 6EQ 


ORDER FORM 

YCI2 


CODE 


TITLE 


OfTV 


PRICE 


TOTAL 












































Cheque/PO No. . 


For 










NAME . 






ADDRES 


e 















CASSETTE ONE 

PROGRAMS FOR ZX81 

"I had. your Invaders.' Re act cassette ... I was 
delighted with this first cassette/ 1 

P. Ruby th on, London 

"Thanks for your Cassette. One you sent ma — some 
sxcellflnt games at a very cheap price!" 

P. Rushton, Leeds 



MACHINE CODE 


BASIC 


REACT 


1 OKrRTG 


INVADERS 


MASTERMIND 


FHAMT0M ALIEN'S 


BASIC HANGMAN 


MAZE OF DEATH 


ROBOTS 


PLANET LANDER 




BOUNCING LITTERS 




BUG SPLAT 





Ideal If you have a IK ZXfil because 

• All the ACTION programmes ar^ In machm$ GodO 

• No-one else sells machine code programs as cheaply 
•Quality cassettes (FUJI or TDK) are used 

•The sequence of II programs Is repeated 4 times, 
just In case a program won't load 

• Cassette One is posted First Class 

• Side 2 contains large screen versions of INVADERS 
and MAZE OF DEATH, naady for wh$n you get the 
16k RAM pack 

Send £3.60 to 

Michael Or win, 28 Bro willow Road, 
Willesden, London NWIO 9QL 

P. 9. Previous customers who did not get the larga screen 
Versions <for 16K) can got free upgrade instructions oy 
fending me a sae 



MICROCOMPUTER COMPONENTS 



LOWEST PRICES - FASTEST DELIVERY 


Dtvlct Mn 


Owk* 


Prlcfl 


0*Ww Prtet 


DivlHfl 


Prltl 


■EMORIES 


mM 


140 


ZILDiZU 'UMILT 


ef&s&£ 


HRI 


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[RTISEMENT 



OFFICIAL 
ORDERS WELCOME 



CREDIT CARD ORDERS 
WELCOME 



QUANTITY 
DISCOUNTS AVAILABLE 



All pncftS esclu-tf* pO«1 a^d i^ftCkirw <ki Qf<Jflr^ yndgi £ 1 ^50p^ And VAT [lS^l 
ALL QHDfcRS OESPAfCHED ON DAY OF RECEIPT WITH FUL.l RE F UND FOR OUt 



OF STOCK ITEMS IF REQUESTED 
24-fiouf Toiflj>hone Credii Card Ordet* 



MIDWICH COMPUTER CO, LTD. 

(Dept YC) 
HEWITT HOUSE, NORTH GATE STREET, 
BURY $T, EDMUNDS, SUFFOLK IP33 1 HQ 
TELEPHONE: (0284) 701 321 TELEX: 81 7870 



96 YOUR COMPUTER, DECEMBER 19flt 



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electronics 



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100 ,ds FROM ARCHWAY STATION & 9 BUS ROUTES 

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YOUR SOUNDEST CONNECTION IN THE WORLD OF COMPUTERS 



PET 



Sfe? 



n t- UK101 



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4032 32K RAM 
4040 Dual Drive Disk 

The new PET printer . 
4022 BO column tracks feed, 
3023 B0 column friction fwd. 
C2N Caisotte Unit. 

For the business .nyn we stock 
the 8000 fange int. 8032 and 
flOSG with daisy wh«l printers 
cornirtg soon. 



32K SYSTEMS AVAILABLE FROM ONLY £1,499 



F VI D E O G 1 : N I E uti h** m i sk ie^«i » 

Baste, integral Cassette 
Deck.UHFO P, I6K RAM. 
ail TRS8D taaHnes &mpl v 
' I ■ K\ prugs inlo moniior Of UH F 

TV. Wi(h V.U Mfltfif 
MOW WITH LOWER CASE AS 
SJMOAHD f?7fl 

PARALLEL PRINTER INK UFACE INC. CABLE £33 00 

CHROMASOfcJSCS PRQGH AMAfiLE SOUND KIT £24.94 



SOUND KIT I FITTING EXTRAI 

LOWER CASE KIT FITTING EXTRA! 

COLOUR KIT I FITTING EXTFAl , 

EXPANSION BOX WITH /WITHOUT R5232 ■ 

I6K/32K RAM CARD . . .- 

NEW GENIE II NOW AVAILABLE ....... 



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E34.95 

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APPLE 



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II plus 



APPLE II PLUS 

48K Machines 1595 

Disk Drive with Con trotter £3*9 

Disc Drive without C on t roller £289 

Colour Card £69 

Graphics Tablet £425 

Silent type printer £199 

48K system available from £1,786 




PRINTERS 




EPSON MX 80 £359 

DoB-matrin - printer ^ith P^T 
graphics i nt-ef f ace Cen ironies 
parallel and serial. Pel and 
Apolac&miiafibla, Trud 
bidiF«cticwLHl. SO cp& 

EPSON MXS0 FT/ 1 £399 

Dual single $h«ej 'ncdon and 
r r^tT0r, 3 wire h+jd-lJ. (rue 

desoencfefs. 



INTERFACES AND CABLES 

for Apole II Pel 
TRS90 FSS53J. UK101, 
Sharp Supsrboard ail avaiiabtf. 

EPSON MXS0 FTt 2 £440 

An FT/ 1 with high rwolufl&n 
graphics. 

EPSON MX 100 £570 
Friction and tractor feed. 

high resolution graphics, wide, 
carriage 15tt inches. 

5EIKOSHA G P80A £199 

Dot rnatri* 5 * 7, 80 co*unin* 
30 cos. g^phisi, double width 
characters. 



-MONITORS 



GREEN MONITOR V' 
12" BMC Green 
Hilachr professional monitors 
9" Black & White 
12" Black & White 



£96.00 
£175 

£99,95 
£149.00 




tf* r 



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UK 101 Kit Inc 8K memory 

Ready Built Inc 8K memory 

Complete in case 

4K Expansion 8x2114 

Memory Expansion Kit 

Printer Interface 

Sound generator plus 

ROkit 

Cases 

NEW * NEW * NEW 

Chromasonic Sound Kit 

Colour Kit 

32K Dynamic Memory Expansion Kit 

loc Dcno Tgpe & fv» 

Oocunwnation. Se-m h» ov'.oi^. 

PIO and Eprom programmer kit 



ftVC* 



£125 

fl75 

£199 

£10 

£24. SO 

£28,95 
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£24.50 
££3.95 
£89.95 



£2450 



VIC 20 



Colours 

24 total 8 tor characters, 3 for border; 16 
lot screen mixed as you wish. &a$jc colours 
on program keys are black, white, red, blue, 
light blue, grefcn., yellow, and purple. 

Sound 

3 Tone Generator for*musJc 
"Whjte Noise" " Generator for language <a nd 
sound effects. 

Each Generator gives 3 ociaves 
Reproduction is rhrough TV speaker, 

Character/ Line Display 

22 Characters t> v 23 tines 
64 ASCII characters, pel- type graphics 
dwacier set 

Keyboard 

DIN Typewriter keyboard with 8 program 
friable function oossib-i lilies vfa 4 special 
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Peripherals, Accessories 

VI C Data Cassette with special interface to 
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IPET'CBM compatible). 



PRICE ONLY £165 
CASSETTE DECK with 6 free 
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ONLY C34.7r 



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TEACHING 
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Please add VAT )S% to all pnets Posia^e on Lampui^rs fK inters and cassette detks charged al cosl all oiher iiems 
P&P JOp Place your order using your Access or Gardaycard (Mm w\ orde r £5j Trade and export enquiries welcome. 




YOUR COMPUTER. DECEMBER 1961 97 



PD4 digital 
XYplotter 




Standard 
specification includes:- 

• IEEE 488 AH l p LI , El Interface 

♦ Full A4 format • 700 mm/s max. writing speed 

* Suitable for direct connection to PET and any other 
computer 

• Optional software including character generator available 

Price including IEEE Interface £#S390 + VAT 



1 J J. LLOYD INSTRUMENTS LTD. 

I Brook Avenue, Wjru&h. Southampton, S03 6HP. 
1 England. Tel: Lock? Heath 4221 ISTD WB95f 
INSTRUMENTS Telex; 47 7M2 - JAY JAY - 5QT0N 



ADVERTISEMENT INDEX 




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1 



THE ATOM DEALER LIST 

Computer stores are stocking Atoms - there's a list 
below. If there isn't one near you* fill in the coupon and 
we'll rush an Atom to you within 28 days- 

Granite Chips Ltd. Aberdeen 22863, Imsmor 
Holdings, Ayr 58602, Micro Style, Bath 334659, 
Broadway Elect, Bedford 213639. Micro-C 
Birmingham 021-233-1105. Owl Computers, 
Bishaps Siortford 526S2, Microccntre, Bog nor 
Regis 827779. Eltcc Services, Bradford 491372. 
Gamer, Brighton 698424. Electronic Information 
Systems, Bristol 428165, Micrc^C Bristol 
0272-650501, Cambridge Comp Store. Cambridge 
65334. Rhombus, Cambridge 31 2953, CardilTMicros, 
Cardiff 373072, Bellard Elect. Chester 380123. 
Vixon Computer Systems. Cleethorpes 58561, 
Customised Electronics Ltd., Cleveland 247727, 
Emprise. Colchester 865926, Ibek Systems Coventry, 
Lendac Data Systems, Dublin 37052. Silicon Centre, 
Edinburgh 332 5277. Highland Microcomputer, 
Forres 73505, H.C.C.S. Associates. Gateshead 
821924. Mikroironic, Germany 05 31 72 223. Esco 
Computing, Glasgow 204 1811. Computer Shack Ltd., 
Gloucester 5 84343. Control Universal, Harlow 
31604, U nitron Elect, Haslington. Castle Elect., 
Hastings 437875, Currys Micro Systems, High 
Wycombe 3643 1. Northern Micro, Huddersfield 
892062. Customised Electronics, Leeds 792332, 
Micro-C, Leeds44660L D,A. Computers, Leicester 
549407, Micro-C, Leicester 546224, MicrodigitaL 
Liverpool 236 0707. Barrie Elect, EC3 488 3316. 
Eurocalc, London 729 4555-9. Group 70, El 8 
352 7333. Microage, North London 959 7119. 
Ragnorak Electronic Systems, E2 981 2748. Sinclair 
Equip. InL (Export), Wl 235 9649. OFF Records. 
SW12 674 1205. Technomatic, NWI0 7230233. 
Micro-C, Luton 425079. Micro-C, Ace Business 
Comp. Maidstone 677947. Manchester 334-0144, 
NSC Comp Shops* Manchester. 832 2269. 
Customised Electronics, Middles bo rough 247727. 
Compshop, New Barnet 441 2922. Micro-C, New 
Maiden 949 209 l r Newbear Computing Store^ 
Newbury 30505. H.C.C.S., Newcastle 821924. 
Newcastle Comp Services, Newcastle 761 158. Anglia 
Comp Centre, Norwich 29652. Leasalink Viewdata. 
Nottingham 396976- Micro-C, Nottingham 41 2455. 
J.A.D. International Services* Plymouth 62616. 
R.D.S. Electrical. Portsmouth 812478. Computers 
for AIL Romford 60725, Intelligent Artifacts, 
Royston Arlington 689, Owl Computers, 
Saw bridge worth 723848. Computer Facilities, 
Scunthorpe 63167. Datron Micro Centre, Sheffield 
585 490. Superior Systems, Sheffield 755005. 
Micro-C. Southampton 29676, Q-TEC Systems, 
Stevenage 65385, 3D Computers. Surbiton (01 ) 337 
43 17. Computer Supplies, Swansea 290047. Abacus 
Micro Comp., Tonbridge Paddock Wood 386 L 
Bellard Electronics Ltd,, Upton 380123, Northern 
Comp, Warrington 601683. Compass Design. Wigan 
Standish 426252. Date* Micros. Worthing 39290. 

SEE OUR ADVERTISEMENT ON PAGE 



SA YOUR COM PUTER, DECEMBER 1331 






■HI 



Hi 



•BZKSS *& 




g^ 




nf *^--' 



V-->. M I 



.. 




TCTTn n 




«?bq T5n"a^ 






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CHOOSE jITOM POWER 

At work or play- everything you need in o personal computer 



The Atom is a machine to be used. 
Every day, day after day. If ■ a full 
function machine- check the 
specification again j t others. Iff 
rugged, easy to operate built to last 
and features a full-size typewriter 
keyboard. 
Ju st lock at tome of the features! 

• More hardware support than any other 
microcomputer * Su^rfast BASIC -can be 
updated to BBC BASIC ij required 

• High resolute and comprehensive 
graphics ideal for games programmers and 
players* •Integral printer connection* 

• Software available for garner education, 
maths, graphs, business, word process uig, etc 

• Other language* Pascal. FORTH LISP 

• I/O port [or control of externa I devices 

• Built-in loudspeaker • Cassette interlace 

• Full service/repair facility • Users club B 

" L-ip-^nde-tf wmop art? 



Optional Extraj 

# Network lacUity withEconet 

♦ Disk ♦ PAL UHF colour en coder 

• Add-on cards include 32K memory, 
analogue to digital, viewdala VDU. disk 
controller, daisywheel printer, plus many, 
many more! • Power supply 

IHEE MANUAL 

The Atoms highly acclaimed manual comes 
be* with every Atom and leaves nothing out In 
just a while you'll be completely at ease with 
your new machine 1 Wi thin hours you' U be 
writing your awn programs 




ATOM SOFTWARE is designed and produced by Acomsoft, a 

division of Acorn Computers, Trust the 
manufacturer to get the very best from its 
own. product. Cuuent software includes 

word processing, maths packs 
over 30 games, database. 
Forth and business packages. 




Write to Acomsoft, 4a Market Hill, 
Cambridge for full details and prices, 



YOU AND YOUH CHILDREN 

More and mote schools cere buying Atom*. 
More and more children wil] leant On an Atom, 
You can give them that extra familiarity with an 
Atom in die home. 




WUIVIrUltK CAMBRIDGf CB2 3NJ 

Wh*?, yoM ocdei youi Atom we wiU include 

Ifutt dvtoik ot aU raJfmrc pack* artd the 

I To: Acorn Computer Limited 4A Market Hill, t 
Cambridge CB23NJ. 

II pTidote a chequ*/posM order (or £ i 
Pleatedgh.l my Acceas.'' 

i fiaiclaycard No , | 

Signature . . ........ K - 

I Namefpiease phnt) I 

IAddnu 
! i-ir.a.l.a4r..ir.l..r------------------- 1 

- Telephone Number . 

| AmpiivndNo 1 103810 VAT No 2] 5 400220 

lt*mprk»ire. 

itiMMia a— THT+rar in»h ■ 
aSHESs*^ EUSBB 
aitAri __ I 

IAuiti Art«Mbi«d K K i 3 1 50 . 
BJQMf 3KWUM ' I 
tonAwriJ H'lSfK #£389 » 

TOTAL 



SEE OUR DEALER LIST ON PAGE 98 




Vfc^) 



See it here, buy it now 

AT YOUR LOCAL 
BRANCH TODAY! 

llMlhWlWTi Byhshop Gompu»N*rtd 9*/96 Hurst &r &5 4TD Tvl^O^l 622 7 149 London Bylathop Com pule rfarwi 32* EwiSnn Hood London Wt W^1^9?05OS Naltlnphom Qy|«rh»Conv*iMind 
92* UpDer Fsri.aT*ne5l M3i -jL^ TW:0H?4C&76 MineflHtar ByWwp Gflmpuwrta'id n Gneway house PiccadilrySta'wr, Appioacft tot 051 ^i6i?37 Qlaagow B>*s*Dp GcmpuSwiand Uagrel 
H<XJS* 6LWalsrlDo5l.C2 7BP Tot 0*1 22 1 7409 

Amom&nrollha-Conwt aat_ Group of Companies